Web Services Business Process Execution Language Version 2.0
Committee Draft, 01 12108th8 SeptemberNovemberDecember October
2005
Document identifier:
wsbpel-specification-draft-01
Location:
http://www.oasis-open.org/apps/org/workgroup/wsbpel/
Editors:
Assaf Arkin <arkin@intalio.com><arkin@intalio.com>
Sid
Askary <saskary@nuperus.com>
Ben Bloch <ben_b54@hotmail.com>
Francisco Curbera,
IBM <curbera@us.ibm.com>
Yaron Goland, BEA <ygoland@bea.com>
Neelakantan Kartha,
Sterling Commerce <N_Kartha@stercomm.com>
Canyang Kevin Liu,
SAP <kevin.liu@sap.com>
Vinkesh Mehta, Deloitte <vmehta@deloitte.com>
Prasad Yendluri,
webMethods <pyendluri@webmethods.com>
Alex Yiu,
Oracle <alex.yiu@oracle.com>
Alexandre
Alves, BEA <aalves@bea.com>
Vinkesh
Mehta, Deloitte <vmehta@deloitte.com>
Contributors:
{FirstName} {Last Name}, {Organization}
Editor’s Notes – KevinL – this section should be consolidated with Appendix H
This document defines a notation for specifying business process behavior based on Web Services. This notation is called Web Services Business Process Execution Language (abbreviated to WS-BPEL in the rest of this document). Processes in WS-BPEL export and import functionality by using Web Service interfaces exclusively.
Business processes can be described in two ways. Executable business processes model actual behavior of a participant in a business interaction. Business protocols, in contrast, use process descriptions that specify the mutually visible message exchange behavior of each of the parties involved in the protocol, without revealing their internal behavior. The process descriptions for business protocols are called abstract processes. WS-BPEL is meant to be used to model the behavior of both executable and abstract processes.
WS-BPEL provides a language for the formal specification of business processes and business interaction protocols. By doing so, it extends the Web Services interaction model and enables it to support business transactions. WS-BPEL defines an interoperable integration model that should facilitate the expansion of automated process integration in both the intra-corporate and the business-to-business spaces.
This is a draft version of the WS-BPEL TC specification, updated from the origninal BPEL4WS V1.1 specification dated May 5, 2003 that was submitted to the WS BPEL TC. See: http://www.oasis-open.org/apps/org/workgroup/wsbpel/download.php/2046/BPEL%20V1-1%20May%205%202003%20Final.pdf
If you are on the <wsbpel@lists.oasis-open.org> list for committee members, send comments there. If you are not on that list, subscribe to the <wsbpel-comment@lists.oasis-open.org> list and send comments there. To subscribe, send an email message to <mailto:wsbpel-comment-request@lists.oasis-open.org> with the word "subscribe"as the body of the message.
For information on whether any patents have been disclosed that may be essential to implementing this specification, and any offers of patent licensing terms, please refer to the Intellectual Property Rights section of the WS-BPEL TC web page http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsbpel
Copyright © 2004 OASIS Open, Inc. All Rights Reserved.
Table of Contents
1. Introduction
3. Relationship with Other Specifications
4. This Section Has Been Deleted
5. Core Concepts and Usage Patterns
6. Defining a Business Process
6.1. Initial Example
6.2. The Structure of a Business Process
6.4. The Lifecycle of a Business Process
7. Partner Link Types, Partner Links, and Endpoint References
7.1. Partner Link Types
7.2. Partner Links
7.3. This Section Has Been Deleted
7.4. Endpoint References
8.1. Motivation
8.2. Defining Properties
9.1. Expressions
9.2. Variables
9.3. Assignment
10. Correlation
10.1. Message Correlation
10.2. Defining and Using Correlation Sets
11. Basic Activities
11.1. Standard Attributes for Each Activity
11.2. Standard Elements for Each Activity
11.3. Invoking Web Service Operations
11.4. Providing Web Service Operations
11.5. Updating Variable Contents
11.6. Signaling Faults
11.7. Waiting
11.8. Doing Nothing
12.1. Sequence
12.2. If
12.3. While
12.4. Pick
12.5. Flow
13. Scopes
13.1. Data Handling and Partner Links
13.2. Error Handling in Business Processes
13.3. Compensation Handlers
13.4. Fault Handlers
13.5. Event Handlers
13.6. Isolated Scopes
14. Extensions for Executable Processes
14.1. Expressions
14.2. Variables
14.3. Assignment
14.4. Correlation
14.5. Web Service Operations
14.6. Terminating a Service Instance
14.7. Compensation
14.8. Event Handlers
15. WS-BPEL Abstract Processes
15.1. The Common Base
15.2
15.2
Abstract Process Profiles and the Semantics of Abstract ProcessesAbstract Process
Profiles and the semantics of Abstract ProcessesVariablesVariables
15.2. Assignment
15.3. Abstract Process Profile for
Observable Behavior15.3 Abstract
Process Profile for…(refactoring AP1.1, issue 82.3)
Observer Behavior
15.4 Abstract Process Template
Profile15.4 Abstract Process Profile for… (new
profile, issue 82.2)Template
Profile
16. Examples
16.1. Shipping Service
16.2 Ordering Service16.2
Ordering Service
16.3. Loan Approval16.32.
Loan Approval
16.4. Multiple Start Activities16.43.
Multiple Start Activities
Appendixes
C. XSD Schemas
D. Notices
E. Intellectual Property Rights
G. References
H. Committee Members (Non-Normative)
1. Introduction
The goal of the Web Services effort is to achieve universal interoperability between applications by using Web standards. Web Services use a loosely coupled integration model to allow flexible integration of heterogeneous systems in a variety of domains including business-to-consumer, business-to-business and enterprise application integration. The following basic specifications originally defined the Web Services space: SOAP, Web Services Description Language (WSDL), and Universal Description, Discovery, and Integration (UDDI). SOAP defines an XML messaging protocol for basic service interoperability. WSDL introduces a common grammar for describing services. UDDI provides the infrastructure required to publish and discover services in a systematic way. Together, these specifications allow applications to find each other and interact following a loosely coupled, platformindependent model.
Systems
integration requires more than the ability to conduct simple interactions by
using standard protocols. The full potential of Web Services as an integration platform
will be achieved only when applications and business processes are able to
integrate their complex interactions by using a standard process integration model. The
interaction model that is directly supported by WSDL is essentially a stateless model of
synchronous or uncorrelated asynchronous interactions. Models for business
interactions typically assume sequences of peer-to-peer message exchanges, both
synchronous and asynchronous, within stateful, long-running interactions
involving two or more parties. To define such business interactions, a formal
description of the message exchange protocols used by business processes in
their interactions is needed. Mutually visible message exchange behavior of each
of the parties involved can be described using an Abstract Process, without
revealing their internal implementation The
definition of such business protocols involves precisely specifying
the mutually visible message exchange behavior of each of the parties involved
in the protocol, without revealing their internal
implementation. There are two good reasons to separate the
public aspects of business process behavior from internal or private aspects. One is that businesses
obviously do not want to reveal all their internal decision making and data management to
their business partners. The other is that, even where this is not the case,
separating public from private process provides the freedom to change private aspects
of the process implementation without affecting the visible
behaviorpublic business protocol.
Visible behavior must clearly be described in a
platform-independent manner and may capture behavioral aspects that have
cross-enterprise business significance. Business protocols must
clearly be described in a platform-independent manner and must capture all
behavioral aspects that have cross-enterprise business significance. Each
participant can then understand and plan for conformance to the business
protocol without engaging in the process of human agreement that adds so much
to the difficulty of establishing cross-enterprise automated business processes
today.
What are the concepts required to describe business processesprotocols?
And what is the relationship of these concepts to those required to describe
executable processes? To answer these questions, consider the following::
·
Business protocols processes invariably
include data-dependent behavior. For example, a supply-chain processprotocol
depends on data such as the number of line items in an order, the total value
of an order, or a deliver-by deadline. Defining business intent in these cases
requires the use of conditional and time-out constructs.
·
The ability to specify exceptional conditions and
their consequences, including recovery sequences, is at least as important for
business protocolsprocesses as
the ability to define the behavior in the "all goes well" case.
·Long-running
interactions include multiple, often nested units of work, each with its own
data requirements. Business processesprotocols
frequently require cross-partner coordination of the outcome (success or
failure) of units of work at various levels of granularity.
If we wish to provide precise predictable
descriptions of service behavior for crossenterprise business protocols, we
need a rich process description notation with many features reminiscent of an
executable language. The key distinction between public message exchange
protocols and executable internal processes is that internal processes handle
data in rich private ways that need not be described in public protocols.
In thinking about the data handling aspects of
business protocols it is instructive to consider the analogy with network
communication protocols. Network protocols define the shape and content of the
protocol envelopes that flow on the wire, and the protocol behavior they
describe is driven solely by the data in these envelopes. In other words, there
is a clear physical separation between protocol-relevant data and
"payload" data. The separation is far less clear cut in business
protocols because the protocol-relevant data tends to be embedded in other
application data.
WS-BPEL uses a notion of message properties , which
are a type of variable property, to identify
protocol-relevant data embedded in messages. Properties can be viewed as "transparent"
data relevant to public aspects as opposed to the "opaque" data that
internal/private functions use. Transparent data affects the public business
protocol in a direct way, whereas opaque data is significant primarily to
back-end systems and affects the business protocol only by creating
nondeterminism because the way it affects decisions is opaque. We take it as a
principle that any data that is used to affect the behavior of a business
protocol must be transparent and hence viewed as a property.
The implicit effect of opaque data manifests itself
through nondeterminism in the behavior of services involved in business
protocols. Consider the example of a purchasing protocol. The seller has a
service that receives a purchase order and responds with either acceptance or
rejection based on a number of criteria, including availability of the goods
and the credit of the buyer. Obviously, the decision processes are opaque, but
the fact of the decision must be reflected as behavior alternatives in the external
business protocol. In other words, the protocol requires something like an if
activity in the behavior of the seller's service but the selection of the
branch taken is nondeterministic. Such nondeterminism can be modeled by
allowing the assignment of a nondeterministic or opaque value to a message
property, typically from an enumerated set of possibilities. The property can
then be used in defining conditional behavior that captures behavioral
alternatives without revealing actual decision processes. WS-BPEL explicitly
allows the use of nondeterministic data values to make it possible to capture
the essence of public behavior while hiding private aspects.
·
The basic concepts of WS-BPEL can be applied in one of two
ways
(abstract or executable):.
A WS-BPEL abstract process is a partially specified process that is not intended to be executed and that must be explicitly declared as ‘abstract’. Whereas executable processes are fully concretized and thus can be executed, an abstract process may abstract away some of the required concrete operational details expressed by a fully executable artifact.
All the constructs of executables processes are made available to abstract processes; consequently, executable and abstract WS-BPEL processes share the same expressive power. In addition to the features available in executable processes, abstract processes provide two mechanisms for abstracting away operational details: (1) omission and (2) the use of explicit opaque tokens. Although a particular abstract process definition might contain complete information that would render it executable if interpreted as an executable process, its abstract status states that any concrete realizations of it are permitted to perform additional processing steps that are not relevant to the audience to which it has been given.
Abstract processes serve a descriptive role, with more than one possible use case. One such use case might be to describe the visible behavior of some or all of the services offered by an executable process. Another use case would be to define a process template that embodies domain-specific best practices. Such a process template would capture essential process logic in a manner compatible with a design-time representation, while excluding execution details to be completed when mapping to an executable process.
Regardless of the specific use case and purpose, all abstract processes share a common syntactic base. They have different requirements for the level of opacity and restrictions on which parts of a process definition may be omitted or hidden. Tailored uses of abstract processes have different effects on the consistency constraints – or the constraints required for a valid executable process that are not enforceable by the XML Schema – and on the semantics of that process.
A common base specifies the features that define the syntactic universe of abstract processes. Given this common base, a usage profile provides the necessary specializations and semantics based on executable WS-BPEL for a particular usage area of an abstract process.
Abstract
processes serve a descriptive role, with more than one possible use
case. One such use case for an abstract process might be to describe the
publicly visible behavior of some or all of the services an executable
process offers (represented by "myRole" in the relevant partnerLinks).
In one particular usage scenario, another use case might be
to define a process "template" that may embody domain-specific best practices.
For
example, such a process "template" could capture some essential process
logic while leaving out operational details that will be concretized
when mapping the partial process specification to a fully executable
artifact.
Regardless
of the purpose, all abstract processes share a common syntactic
base. However, they actually have different, possibly conflicting,
requirements for the levels of opacity and restrictions or relaxations
on which parts of a process definition may be omitted or hidden,
i.e. the overall level of incompleteness. Hence, different uses of
abstract processes have different effects on the consistency constraints
required in executable processes, and on the semantics of that
process. We use ‘consistency constraints’ to refer to constraints required
for a valid executable WS-BPEL process that are not enforceable by
the XML Schema, such as requiring at least one receive with ‘createInstance’
set to true or that every link with a source activity must
have a target activity. In order to address this flexibility, a ‘base-and-profiles’
approach is provided in section 15 for defining abstract
processes.
A
common base specifies the features that define the syntactic universe
of
abstract processes. However, the base lacks well-defined semantics. Given
this common base, a usage profile provides the necessary specializations
and the semantics based on executable WS-BPEL for a particular
usage area of an abstract process. For example, one profile might
focus on publicly visible behavior; another profile might focus on
process templates of particular granularity.A WS-BPEL
process can define a business protocol role, using the notion of abstract
process. For example, in a supply-chain protocol, the buyer and the seller are
two distinct roles, each with its own abstract process. Their relationship is
typically modeled as a partner link. Abstract processes use all the concepts of
WS-BPEL but approach data handling in a way that reflects the level of
abstraction required to describe public aspects of the business protocol.
Specifically, abstract processes handle only protocol-relevant data. WS-BPEL
provides a way to identify protocol-relevant data as message properties. In
addition, abstract processes use nondeterministic data values to hide private
aspects of behavior.
As mentioned earlier iIt
is also possible to use WS-BPEL to define an executable business process. The
logic and state of the process determine the nature and sequence of the Web
Service interactions conducted at each business partner, and thus the
interaction protocols. While a WS-BPEL process definition is not required to be
complete from a private implementation point of view, the language effectively
defines a portable execution format for business processes that rely
exclusively on Web Service resources and XML data. Moreover, such processes
execute and interact with their partners in a consistent way regardless of the
supporting platform or programming model used by the implementation of the
hosting environment.
Even where private implementation aspects use
platform-dependent functionality, which is likely in many if not most realistic
cases, the continuity of the basic conceptual model between abstract and
executable processes in WS-BPEL makes it possible to export and import the
public aspects embodied in business protocolsabstract processes as
process or role templates while maintaining the intent and structure of the
protocols. This is arguably the most attractive prospect for the use of WS-BPEL
from the viewpoint of unlocking the potential of Web Services because it allows
the development of tools and other technologies that greatly increase the level
of automation and thereby lower the cost in establishing cross-enterprise
automated business processes.
In summary, we believe that the two usage patterns of
business protocol description and executable business process description abstract
business process and executable business process
descriptions require a common core of process description
concepts. In this specification we clearly separate the core concepts from the
extensions required specifically for the two usage patterns. The WS-BPEL
specification is focused on defining the common core, and adds only the
essential extensions required for each usage pattern.
WS-BPEL defines a model and a grammar for describing the behavior of a business process based on interactions between the process and its partners. The interaction with each partner occurs through Web Service interfaces, and the structure of the relationship at the interface level is encapsulated in what we call a partner link. The WS-BPEL process defines how multiple service interactions with these partners are coordinated to achieve a business goal, as well as the state and the logic necessary for this coordination. WS-BPEL also introduces systematic mechanisms for dealing with business exceptions and processing faults. Finally, WS-BPEL introduces a mechanism to define how individual or composite activities within a process are to be compensated in cases where exceptions occur or a partner requests reversal.
WS-BPEL is layered on top of several XML specifications: WSDL 1.1, XML Schema 1.0, and XPath1.0. WSDL messages and XML Schema type definitions provide the data model used by WS-BPEL processes. XPath provides support for data manipulation. All external resources and partners are represented as WSDL services. WS-BPEL provides extensibility to accommodate future versions of these standards, specifically the XPath and related standards used in XML computation.
2. Notational Conventions
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119].
Namespace URIs of the general form "some-URI" represent some application-dependent or context-dependent URI as defined in [RFC 2396].
This specification uses an informal syntax to describe the XML grammar of the XML fragments that follow:
· The syntax appears as an XML instance, but the values indicate the data types instead of values.
· Grammar in bold has not been introduced earlier in the document, or is of particular interest in an example.
· <-- description --> is a placeholder for elements from some "other" namespace (like ##other in XSD).
· Characters are appended to elements, attributes, and as follows: "?" (0 or 1), "*" (0 or more), "+" (1 or more). The characters "[" and "]" are used to indicate that contained items are to be treated as a group with respect to the "?", "*", or "+" characters.
· Elements and attributes separated by "|" and grouped by "(" and ")" are meant to be syntactic alternatives.
· The XML namespace prefixes (defined below) are used to indicate the namespace of the element being defined.
· Examples starting with <?xml contain enough information to conform to this specification; other examples are fragments and require additional information to be specified in order to conform.
· XSD schemas and WSDL definitions are provided as a formal definition of grammars [XML Schema Part 1] and [WSDL 1.1].
This specification uses a number of namespace prefixes throughout; their associated URIs are listed below. Note that the choice of any namespace prefix is arbitrary and not semantically significant.
· xsi - "http://www.w3.org/2001/XMLSchema-instance"
· xsd - "http://www.w3.org/2001/XMLSchema"
· wsdl - "http://schemas.xmlsoap.org/wsdl/"
· plnk – http://schemas.xmlsoap.org/ws/2004/03/partner-link/”
· bpws – “http://schemas.xmlsoap.org/ws/2004/03/business-process/”
3. Relationship with Other Specifications
WS-BPEL depends on the following XML-based specifications: WSDL 1.1, XML Schema 1.0 and XPath 1.0.
Among these, WSDL has the most influence on the WS-BPEL language. The WS-BPEL process model is layered on top of the service model defined by WSDL 1.1. At the core of the WS-BPEL process model is the notion of peer-to-peer interaction between services described in WSDL; both the process and its partners are modeled as WSDL services. A business process defines how to coordinate the interactions between a process instance and its partners. In this sense, a WS-BPEL process definition provides and/or uses one or more WSDL services, and provides the description of the behavior and interactions of a process instance relative to its partners and resources through Web Service interfaces. That is, WS-BPEL defines the message exchange protocols followed by the business process of a specific role in the interaction.
The definition of a WS-BPEL business process also follows the WSDL model of separation between the abstract message contents used by the business process and deployment information (messages and portType versus binding and address information). In particular, a WS-BPEL process represents all partners and interactions with these partners in terms of abstract WSDL interfaces (portTypes and operations); no references are made to the actual services used by a process instance.
However, the abstract part of WSDL does not define the constraints imposed on the communication patterns supported by the concrete bindings. Therefore a WS-BPEL process may define behavior relative to a partner service that is not supported by all possible bindings, and it may happen that some bindings are invalid for a WS-BPEL process definition.
While WS-BPEL attempts to provide as much compatibility with WSDL 1.1 as possible there are three areas where such compatibility has proven impossible. One area, discussed later in this document, is in fault naming. Another area is in support for overloaded operation names in WSDL portTypes. A BPEL processor MUST reject any WSDL portType definition that includes overloaded operation names. This restriction was deemed appropriate as overloaded operations are rare, they are actually banned in the WS-I Basic Profile and supporting them was felt to introduce more complexity than benefit. Finally a WS-BPEL processor MUST reject a WS-BPEL that refers to a portType that contain solicit-response or notification operations as defined in the WSDL 1.1 specification, this requirement MUST be statically enforced.
BPEL does not make any assumptions about the WSDL binding. Constraints, ambiguities, provided or missing capabilities of WSDL bindings are out of scope of this specification.
A WS-BPEL process is a reusable definition that can be deployed in different ways and in different scenarios, while maintaining a uniform application-level behavior across all of them. Note that the description of the deployment of a WS-BPEL process is out of scope for this specification.
Introduction of service reference container (“bpws:service-ref”) is meant to avoid inventing a private WS-BPEL mechanism for web service endpoint references and to provide pluggability of different versions of service referencing or endpoint addressing schemes being used within a BPEL program without having explicit dependency to a particular version of specification.
With respect to [WS-I Basic Profile] (Basic Profile 1.1) all BPEL implementations SHOULD be configurable such that they can participate in Basic Profile 1.1 compliant interactions. A BPEL implementation MAY allow the Basic Profile 1.1 configuration to be disabled, even for scenarios encompassed by the Basic Profile 1.1. At the time this specification was completed, the WSDL v2.0 work was ongoing and not ready for consideration for WS-BPEL v2.0. Future versions of WS-BPEL may provide support for WSDL v2.0.
4. This Section Has Been Deleted
5. Core Concepts and Usage Patterns
As noted in the introduction, we believe that the two usage patterns of business protocol description and executable business process description require a common core of process description concepts. In this specification we clearly separate the core concepts from the extensions required specifically for the two usage patterns. The WS-BPEL specification is focused on defining the common core, and adds only the essential extensions required for each usage pattern. These extensions are described in separate sections (Extensions for Executable Processes and Extensions for Business Protocols).
In a number of cases, the behavior of a process in a certain combination of circumstances is undefined, e.g., when a variable is used before being initialized. In the definition of the core concepts we simply note that the semantics in such cases is not defined.
WS-BPEL takes it as a general principle that compliant implementations MAY choose to perform static analysis to detect and reject process definitions that may have undefined semantics. Such analysis is necessarily pessimistic and therefore might in some cases prevent the use of processes that would not, in fact, create situations with undefined semantics, either in specific uses or in any use.
In the executable usage pattern for WS-BPEL, situations of undefined semantics always result in standard faults in the WS-BPEL namespace. These cases will be described as part of the Extensions for Executable Processes in the specification. However, it is important to note that WS-BPEL uses exactly one standard internal fault for its core control semantics, namely, bpws:joinFailure. This is the only standard fault that plays a role in the core concepts of WS-BPEL. Of course, the occurrence of faults specified in WSDL portType definitions during web service invocation is accounted for in the core concepts as well.
6. Defining a Business Process
6.1. Initial Example
Before describing the structure of business processes in detail, this section presents a simple example of a WS-BPEL process for handling a purchase order. The aim is to introduce the most basic structures and some of the fundamental concepts of the language.
The operation of the process is very simple, and is represented in the following figure. Dotted lines represent sequencing. Free grouping of sequences represents concurrent sequences. Solid arrows represent control links used for synchronization across concurrent activities. Note that this is not meant to be a definitive graphical notation for WS-BPEL processes. It is used here informally as an aid to understanding.
On receiving the purchase order from a customer, the process initiates three tasks concurrently: calculating the final price for the order, selecting a shipper, and scheduling the production and shipment for the order. While some of the processing can proceed concurrently, there are control and data dependencies between the three tasks. In particular, the shipping price is required to finalize the price calculation, and the shipping date is required for the complete fulfillment schedule. When the three tasks are completed, invoice processing can proceed and the invoice is sent to the customer.
The WSDL portType offered by the service to its customers (purchaseOrderPT) is shown in the following WSDL document. Other WSDL definitions required by the business process are included in the same WSDL document for simplicity; in particular, the portTypes for the Web Services providing price calculation, shipping selection and scheduling, and production scheduling functions are also defined there. Observe that there are no bindings or service elements in the WSDL document. A WS-BPEL process is defined "in the abstract" by referencing only the portTypes of the services involved in the process, and not their possible deployments. Defining business processes in this way allows the reuse of business process definitions over multiple deployments of compatible services.
The partner link types included at the bottom of the WSDL document represent the interaction between the purchase order service and each of the parties with which it interacts (see Partner Link Types, Partner Links, and Endpoint References). Partner link types can be used to represent dependencies between services, regardless of whether a WS-BPEL business process is defined for one or more of those services. Each partner link type defines up to two "role" names, and lists the portTypes that each role must support for the interaction to be carried out successfully. In this example, two partner link types, "purchasingLT" and "schedulingLT", list a single role because, in the corresponding service interactions, one of the parties provides all the invoked operations: The "purchasingLT" partner link represents the connection between the process and the requesting customer, where only the purchase order service needs to offers a service operation ("sendPurchaseOrder"); the "schedulingLT" partner link represents the interaction between the purchase order service and the scheduling service, in which only operations of the latter are invoked. The two other partner link types, "invoicingLT" and "shippingLT", define two roles because both the user of the invoice calculation and the user of the shipping service (the invoice or the shipping schedule) must provide callback operations to enable asynchronous notifications to be asynchronously sent ("invoiceCallbackPT" and "shippingCallbackPT" portTypes).
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<definitions targetNamespace="http://manufacturing.org/wsdl/purchase"
xmlns:sns="http://manufacturing.org/xsd/purchase"
xmlns:pos="http://manufacturing.org/wsdl/purchase"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<types>
<xsd:schema > <xsd:import namespace="http://manufacturing.org/xsd/purchase"
schemalocation="http://manufacturing.org/xsd/purchase.xsd"/>
</xsd:schema> </types>
<message name="POMessage">
<part name="customerInfo" type="sns:customerInfo"/>
<part name="purchaseOrder" type="sns:purchaseOrder"/>
</message>
<message name="InvMessage">
<part name="IVC" type="sns:Invoice"/>
</message>
<message name="orderFaultType">
<part name="problemInfo" element=”sns:OrderFault"/>
</message>
<message name="shippingRequestMessage">
<part name="customerInfo" element="sns:customerInfo"/>
</message>
<message name="shippingInfoMessage">
<part name="shippingInfo" element="sns:shippingInfo"/>
</message>
<message name="scheduleMessage">
<part name="schedule" element="sns:scheduleInfo"/>
</message>
<!-- portTypes supported by the purchase order process -->
<portType name="purchaseOrderPT">
<operation name="sendPurchaseOrder">
<input message="pos:POMessage"/>
<output message="pos:InvMessage"/>
<fault name="cannotCompleteOrder"
message="pos:orderFaultType"/>
</operation>
</portType>
<portType name="invoiceCallbackPT">
<operation name="sendInvoice">
<input message="pos:InvMessage"/>
</operation>
</portType>
<portType name="shippingCallbackPT">
<operation name="sendSchedule">
<input message="pos:scheduleMessage"/>
</operation>
</portType>
<!-- portType supported by the invoice services -->
<portType name="computePricePT">
<operation name="initiatePriceCalculation">
<input message="pos:POMessage"/>
</operation>
<operation name="sendShippingPrice">
<input message="pos:shippingInfoMessage"/>
</operation>
</portType>
<!-- portType supported by the shipping service -->
<portType name="shippingPT">
<operation name="requestShipping">
<input message="pos:shippingRequestMessage"/>
<output message="pos:shippingInfoMessage"/>
<fault name="cannotCompleteOrder"
message="pos:orderFaultType"/>
</operation>
</portType>
<!-- portType supported by the production scheduling process -->
<portType name="schedulingPT">
<operation name="requestProductionScheduling">
<input message="pos:POMessage"/>
</operation>
<operation name="sendShipingSchedule">
<input message="pos:scheduleMessage"/>
</operation>
</portType>
<plnk:partnerLinkType name="purchasingLT">
<plnk:role name="purchaseService"
portType="pos:purchaseOrderPT"/>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="invoicingLT">
<plnk:role name="invoiceService"
portType="pos:computePricePT"/>
<plnk:role name="invoiceRequester" portType="pos:invoiceCallbackPT"/>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="shippingLT">
<plnk:role name="shippingService" portType="pos:shippingPT"/>
<plnk:role name="shippingRequester" portType="pos:shippingCallbackPT"/>
</plnk:partnerLinkType>
<plnk:partnerLinkType name="schedulingLT">
<plnk:role name="schedulingService"
portType="pos:schedulingPT"/>
</plnk:partnerLinkType>
</definitions>
The business process for the order service is defined next. There are four major sections in this process definition:
· The <variables> section defines the data variables used by the process, providing their definitions in terms of WSDL message types, XML Schema types (simple or complex), or XML Schema elements. Variables allow processes to maintain state data and process history based on messages exchanged.
· The <partnerLinks> section defines the different parties that interact with the business process in the course of processing the order. The four partnerLinks shown here correspond to the sender of the order (customer), as well as the providers of price (invoicingProvider), shipment (shippingProvider), and manufacturing scheduling services (schedulingProvider). Each partner link is characterized by a partner link type and a role name. This information identifies the functionality that must be provided by the business process and by the partner service for the relationship to succeed, that is, the portTypes that the purchase order process and the partner need to implement.
· The <faultHandlers> section contains fault handlers defining the activities that must be performed in response to faults resulting from the invocation of the assessment and approval services. In WS-BPEL, all faults, whether internal or resulting from a service invocation, are identified by a qualified name. In particular, each WSDL fault is identified in WS-BPEL by a qualified name formed by the target namespace of the WSDL document in which the relevant portType and fault are defined, and the ncname of the fault. It is important to note, however, that because WSDL 1.1 does not require that fault names be unique within the namespace where the operation is defined, all faults sharing a common name and defined in the same namespace are indistinguishable. In spite of this serious WSDL limitation, WS-BPEL provides a uniform naming model for faults, in the expectation that future versions of WSDL will provide a better fault-naming model.
· The rest of the process definition contains the description of the normal behavior for handling a purchase request. The major elements of this description are explained in the section following the process definition.
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<process name="purchaseOrderProcess"
targetNamespace="http://acme.com/ws-bp/purchase"
xmlns="http://schemas.xmlsoap.org/ws/2004/03/business-process/"
xmlns:lns="http://manufacturing.org/wsdl/purchase">
<documentation xml:lang="EN">A simple example of a WS-BPEL process for handling a purchase order.</documentation>
<partnerLinks>
<partnerLink name="purchasing"
partnerLinkType="lns:purchasingLT"
myRole="purchaseService"/>
<partnerLink name="invoicing"
partnerLinkType="lns:invoicingLT"
myRole="invoiceRequester"
partnerRole="invoiceService"/>
<partnerLink name="shipping"
partnerLinkType="lns:shippingLT"
myRole="shippingRequester"
partnerRole="shippingService"/>
<partnerLink name="scheduling"
partnerLinkType="lns:schedulingLT"
partnerRole="schedulingService"/>
</partnerLinks>
<variables>
<variable name="PO" messageType="lns:POMessage"/>
<variable name="Invoice" messageType="lns:InvMessage"/>
<variable name="POFault" messageType="lns:orderFaultType"/>
<variable name="shippingRequest" messageType="lns:shippingRequestMessage"/>
<variable name="shippingInfo" messageType="lns:shippingInfoMessage"/>
<variable name="shippingSchedule" messageType="lns:scheduleMessage"/>
</variables>
<faultHandlers>
<catch faultName="lns:cannotCompleteOrder" faultVariable="POFault" faultMessageType="lns:orderFaultType">
<reply partnerLink="purchasing"
portType="lns:purchaseOrderPT"
operation="sendPurchaseOrder"
variable="POFault"
faultName="cannotCompleteOrder"/>
</catch>
</faultHandlers>
<sequence>
<receive partnerLink="purchasing"
portType="lns:purchaseOrderPT"
operation="sendPurchaseOrder"
variable="PO">
</receive>
<flow>
<documentation> A parallel flow to handle shipping, invoicing and scheduling </documentation>
<links>
<link name="ship-to-invoice"/>
<link name="ship-to-scheduling"/>
</links>
<sequence>
<assign>
<copy>
<from>$PO.customerInfo</from> <to>$shippingRequest.customerInfo</to>
</copy>
</assign>
<invoke partnerLink="shipping"
portType="lns:shippingPT"
operation="requestShipping"
inputVariable="shippingRequest"
outputVariable="shippingInfo">
<sources> <source linkName="ship-to-invoice"/>
</sources>
</invoke>
<receive partnerLink="shipping"
portType="lns:shippingCallbackPT"
operation="sendSchedule"
variable="shippingSchedule">
<sources> <source linkName="ship-to-scheduling"/>
</sources>
</receive>
</sequence>
<sequence>
<invoke partnerLink="invoicing"
portType="lns:computePricePT"
operation="initiatePriceCalculation"
inputVariable="PO">
</invoke>
<invoke partnerLink="invoicing"
portType="lns:computePricePT"
operation="sendShippingPrice"
inputVariable="shippingInfo">
<targets> <target linkName="ship-to-invoice"/>
</targets>
</invoke>
<receive partnerLink="invoicing"
portType="lns:invoiceCallbackPT"
operation="sendInvoice"
variable="Invoice"/>
</sequence>
<sequence>
<invoke partnerLink="scheduling"
portType="lns:schedulingPT"
operation="requestProductionScheduling"
inputVariable="PO">
</invoke>
<invoke partnerLink="scheduling"
portType="lns:schedulingPT"
operation="sendShippingSchedule"
inputVariable="shippingSchedule">
<targets> <target linkName="ship-to-scheduling"/>
</targets>
</invoke>
</sequence>
</flow>
<reply partnerLink="purchasing"
portType="lns:purchaseOrderPT"
operation="sendPurchaseOrder"
variable="Invoice"/>
</sequence>
</process>
6.2. The Structure of a Business Process
This section provides a quick summary of the WS-BPEL syntax. It provides only a brief overview; the details of each language construct are described in the rest of this document.
The basic structure of the language is:
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<process name="ncname" targetNamespace="uri"
abstractProcessProfile="anyURI"?queryLanguage="anyURI"?
expressionLanguage="anyURI"?
suppressJoinFailure="yes|no"?
abstractProcess="yes|no"?xmlns="http://schemas.xmlsoap.org/ws/2004/03/business-process/">
<extensions>?
<extension namespace="anyURI" mustUnderstand="yes|no"/>*</extensions>
<import namespace="uri" location="uri" importType="uri"/>*
<partnerLinks>?
<!-- Note: At least one role must be specified. -->
<partnerLink name="ncname" partnerLinkType="qname"
myRole="ncname"? partnerRole="ncname"?>+
</partnerLink>
</partnerLinks>
<variables>?
<variable name="ncname" messageType="qname"?
type="qname"? element="qname"?/>+
</variables>
<correlationSets>?
<correlationSet name="ncname" properties="qname-list"/>+
</correlationSets>
<faultHandlers>?
<!-- Note: There must be at least one fault handler or default. -->
<catch faultName="qname"? faultVariable="ncname"?
faultMessageType="qname"? faultElement="qname"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
</faultHandlers>
<eventHandlers>?<!-- Note: There must be at least one onEvent or onAlarm handler. --> <onEvent partnerLink="ncname" portType="qname"? operation="ncname" messageType="qname" variable="ncname" messageExchange="ncname"? >* <correlationSets>? <correlationSet name="ncname" properties="qname-list"/>+ </correlationSets> <correlations>? <correlation set="ncname" initiate="yes|join|no"?/>+ </correlations> scope-activity </onEvent> <onAlarm>*
( ( <for expressionLanguage="anyURI"?>duration-expr</for> | <until expressionLanguage="anyURI"?>deadline-expr</until> ) <repeatEvery expressionLanguage="anyURI"?> duration-expr </repeatEvery>?
) |
<repeatEvery expressionLanguage="anyURI"?> duration-expr </repeatEvery> scope-activity </onAlarm></eventHandlers>
activity
</process>
The top-level attributes are as follows:
· abstractProcessProfile. This attribute provides the URI that identifies the profile of an abstract process. It is mandatory for abstract processes.
· queryLanguage. This attribute specifies the default XML query language used for selection of nodes in assignment, property definition, and other uses. The default value for this attribute is: "urn:oasis:names:tc:wsbpel:2.0:sublang:xpath1.0", which represents the usage of XPath 1.0 within WS-BPEL 2.0. The URI of the corresponding XPath 1.0 specification is: http://www.w3.org/TR/1999/REC-xpath-19991116.
· expressionLanguage. This attribute specifies the expression language used in the process. The default value for this attribute is: "urn:oasis:names:tc:wsbpel:2.0:sublang:xpath1.0", which represents the usage of XPath 1.0 within WS-BPEL 2.0. The URI of the corresponding XPath 1.0 specification is: http://www.w3.org/TR/1999/REC-xpath-19991116.
· suppressJoinFailure. This attribute determines whether the joinFailure fault will be suppressed for all activities in the process. The effect of the attribute at the process level can be overridden by an activity using a different value for the attribute. The default for this attribute is "no" at the process level. When this attribute is not specified for an activity, it inherits its value from its closest enclosing activity or from the process if no enclosing activity specifies this attribute.
· exitOnStandardFault. This attribute specifies if the process must exit if a WS-BPEL standard fault other than bpws:joinFailure is encountered[1]. If the value of this attribute is set to “yes”, then the process MUST exit immediately as if an <exit> activity has been reached, when a WS-BPEL standard fault other than bpws:joinFailure is enountered. If the value of this attribute is set to “no”, then the process can handle a standard fault using a fault handler. The default value for this attribute is “no”. When this attribute is not specified on a <scope> it inherits its value from its enclosing <scope> or <process>.
If the value of exitOnStandardFault of a <scope> or <process> is set to “yes”, then a fault handler that explicitly targets the WS-BPEL standard faults MUST NOT be used in that scope. A process definition that violates this condition MUST be detected and rejected by static analysis.
· abstractProcess. This attribute specifies whether the process being defined is abstract (rather than executable). The default for this attribute is "no".
The value of the queryLanguage and expressionLanguage attributes on the
<process> element are global defaults and can be overridden on
specific activities like <assign> using the mechanisms defined later in
this specification. In addition the queryLanguage attribute is also
available for use in defining BPEL property aliases in WSDL. BPEL processors
MUST:
· statically determine which languages are referenced by queryLanguage or expressionLanguage attributes either in the BPEL process definition itself or in any BPEL property definitions in associated WSDLs and
· if any referenced language is unsupported by the BPEL processor then the processor MUST NOT process the submitted BPEL process definition.
Note that: <documentation> construct may be added to virtually all WS-BPEL constructs as the formal way to annotate processes definition with human documentation. Examples of <documentation> construct can be found in previous section. Detailed description of <documention> is provided in next section, as it is a part of “Language Extensibility”.
The token "activity" can be any of the following:
· <receive>
· <reply>
· <invoke>
· <assign>
· <throw>
· <exit>
· <wait>
· <empty>
· <sequence>
· <if>
· <while>
· <repeatUntil>
· <forEach>
· <pick>
· <flow>
·
<forEach>
· <scope>
· <compensate>
· <rethrow>
· <validate>
· <extensionActivity>
The syntax of each of these elements, except <exit>, <compensate> and <rethrow>, is considered in the following paragraphs.
·Although
<exit> is permitted as an interpretation of the token activity, it is
only available in executable processes and as such is defined in the section on
Extensions for Executable Processes.
· <compensate> activity can be used ONLY within a fault handler or a compensation handler (i.e. <catch>, <catchAll> and <compensationHandler> elements).
· <rethrow> activity can be used ONLY within a fault handler (i.e. <catch> and <catchAll> elements).
The <receive> construct allows the business process to do a blocking wait for a matching message to arrive. The portType attribute on the <receive> activity is optional. If the portType attribute is included for readability, the value of the portType attribute MUST match the portType value implied by the combination of the specified partnerLink and the role implicitly specified by the activity (See also partnerLink description in the next section). The optional messageExchange attribute is used to associate a <reply> activity with a <receive> activity. (For details of messageExchange, please see “Providing Web Service Operations” section).
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<receive partnerLink="ncname" portType="qname"? operation="ncname"
variable="ncname"? createInstance="yes|no"?
messageExchange="ncname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|join|no"?/>+
</correlations> <fromPart part="ncname" toVariable="ncname"/>*
</receive>
The <reply> construct allows the business process to send a message in reply to a message that was received through a <receive>. The combination of a <receive> and a <reply> forms a request-response operation on the WSDL portType for the process. The portType attribute on the <reply> activity is optional. If the portType attribute is included for readability, the value of the portType attribute MUST match the portType value implied by the combination of the specified partnerLink and the role implicitly specified by the activity (See also partnerLink description in the next section). The optional messageExchange attribute is used to associate a <reply> activity with an inbound message activity, such as, <receive>, <onMessage> and <onEvent>. (For details of messageExchange, please see “Providing Web Service Operations” section).
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<reply partnerLink="ncname" portType="qname"? operation="ncname"
variable="ncname"? faultName="qname"?
messageExchange="ncname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|join|no"?/>+
</correlations> <toPart part="ncname" fromVariable="ncname"/>*
</reply>
The <invoke> construct allows the business process to invoke a one-way or requestresponse operation on a portType offered by a partner. The portType attribute on the <invoke> activity is optional. If the portType attribute is included for readability, the value of the portType attribute MUST match the portType value implied by the combination of the specified partnerLink and the role implicitly specified by the activity (See also partnerLink description in the next section).
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<invoke partnerLink="ncname" portType="qname"? operation="ncname"
inputVariable="ncname"? outputVariable="ncname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|join|no"?
pattern="in|out|out-in"/>+
</correlations>
<catch faultName=“qname”? faultVariable="ncname"?
faultMessageType="qname"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
<compensationHandler>?
activity
</compensationHandler> <toPart part="ncname" fromVariable="ncname"/>* <fromPart part="ncname" toVariable="ncname"/>*
</invoke>
The <assign> construct can be used to update the values of variables with new data. An <assign> construct can contain any number of elementary assignments, including <copy> assign elements or data update operations defined as extension under other namespaces. The syntax of the assignment activity is:
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<assign validate="yes|no"? standard-attributes>
standard-elements
(<copy> from-spec to-spec </copy> | <extensibleAssign> ...assign-element-of-other-namespace... </extensibleAssign>) +
</assign>
The <validate> construct can be used to validate the values of variables against their associated XML and WSDL data definition. The construct has a variables attribute, which points to the variables being validated. The syntax of the validate activity is:
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<validate variables="ncname-lists" standard-attributes>
standard-elements
</validate> />
The <throw> construct generates a fault from inside the business process.
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<throw faultName="qname" faultVariable="ncname"? standard-attributes>
standard-elements
</throw>
The <wait> construct allows you to wait for a given time period or until a certain time has passed. Exactly one of the expiration criteria must be specified.
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<wait standard-attributes>
standard-elements ( <for expressionLanguage="anyURI"?>duration-expr</for> | <until expressionLanguage="anyURI"?>deadline-expr</until> )
</wait>
The <empty> construct allows you to insert a "no-op" instruction into a business process. This is useful for synchronization of concurrent activities, for instance.
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<empty standard-attributes>
standard-elements
</empty>
New activities can be introduced for use in BPEL by placing them inside of the extensionActivity element. The contents of an extensionActivity element MUST be a single element that MUST make available BPEL's standard-attributes and standard-elements.
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<extensionActivity> <???? standard-attributes> standard-elements </????></extensionActivity>
The <sequence> construct allows you to define a collection of activities to be performed sequentially in lexical order.
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<sequence standard-attributes>
standard-elements
activity+
</sequence>
The <if> construct allows you to select exactly one branch of activity from a set of potential choices.
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<if standard-attributes>
standard-elements <condition expressionLanguage="anyURI"?> ... bool-expr ... </condition> <then>
activity </then> <elseif>* <condition expressionLanguage="anyURI"?> ... bool-expr ... </condition>
activity </elseif> <else>? activity
</else>
</if>
The <while> construct allows you to indicate that an
activity is to be repeated until aas long as a certain
success criteria has beenis met.
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<while standard-attributes> standard-elements <condition expressionLanguage="anyURI"?> ... bool-expr ... </condition>
activity
</while>
The <repeatUntil> constructs allows you to indicate the repeated performance of a specified iterative activity. The iterative activity will continue to be performed so long as after it executes the given Boolean <repeatUntil> condition holds true.
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<repeatUntil standard-attributes> standard-elements activity <condition expressionLanguage="anyURI"?> ... bool-expr ... </condition></repeatUntil>
The <forEach> construct is an iterator that will repeat its contained scope activity exactly N+1 times where N equals the <finalCounterValue> minus the <startCounterValue>. If parallel="yes" then this is a parallel foreach where the N+1 instances of the enclosed scope activity will occur in parallel. In essence an implicit flow is dynamically created with N+1 copies of the foreach's scope activity as children. If <completionCondition> is specified within the <forEach> construct, the forEach activity MAY be completed without executing or finishing all the branches specified. The details of the early completion condition is specified within the <branches> construct.
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<forEach counterName="ncname" parallel="yes|no" standard-attributes> standard-elements
<iterator> <startCounterValue expressionLanguage="anyURI"> ... </startCounterValue> <finalCounterValue expressionLanguage="anyURI"> ... </finalCounterValue>
</iterator>
<completionCondition> <branches expressionLanguage="URI"? countCompletedBranchesOnly="yes|no"?> an-integer-expression </branches> </completionCondition>? scope-activity</foreach>
The <pick> construct allows you to block and wait for a suitable message to arrive or for a time-out alarm to go off. When one of these triggers occurs, the associated activity is performed and the pick completes.
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<pick createInstance="yes|no"? standard-attributes>
standard-elements
<onMessage partnerLink="ncname" portType="qname"?
operation="ncname" variable="ncname"?
messageExchange="ncname"? >+
<correlations>?
<correlation set="ncname" initiate="yes|join|no"?/>+
</correlations> <fromPart part="ncname" toVariable="ncname"/>*
activity
</onMessage>
<onAlarm>* ( <for expressionLanguage="anyURI"?>duration-expr</for> | <until expressionLanguage="anyURI"?>deadline-expr</until> )
activity
</onAlarm>
</pick>The portType attribute on the <onMessage> activity is optional. If the portType attribute is included for readability, the value of the portType attribute MUST match the portType value implied by the combination of the specified partnerLink and the role implicitly specified by the activity (See also partnerLink description in the next section). The optional messageExchange attribute is used to associate a <reply> activity with a <onMessage> activity. (For details of messageExchange, please see “Providing Web Service Operations” section).
The <flow> construct allows you to specify one or more activities to be performed concurrently. Links can be used within concurrent activities to define arbitrary control structures.
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<flow standard-attributes>
standard-elements
<links>?
<link name="ncname">+
</links>
activity+
</flow>
The <scope> construct allows you to define a nested activity with its own associated variables, fault handlers, and compensation handler.
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<scope isolated="yes|no" standard-attributes>
standard-elements <partnerLinks>? ... see above under <process> for syntax ...
</partnerLinks>
<variables>?
... see above under <process> for syntax ...
</variables>
<correlationSets>?
... see above under <process> for syntax ...
</correlationSets>
<faultHandlers>?
... see above under <process> for syntax ...
</faultHandlers>
<compensationHandler>?
... see above under <process> for syntax ...
</compensationHandler>
<terminationHandler>?
...
</terminationHandler>
<eventHandlers>?
...
</eventHandlers>
activity
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The <compensate> construct is used to invoke compensation on an inner scope that has already completed normally. This construct can be invoked only from within a fault handler or another compensation handler.
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<compensate scope="ncname"? standard-attributes>
standard-elements
</compensate>
Note that the "standard-attributes" referred to above are:
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name="ncname"? suppressJoinFailure="yes|no"?
where the default values are as follows:
· name: No default value (that is, the default is unnamed)
· suppressJoinFailure: When this attribute is not specified for an activity, it inherits its value from its closest enclosing activity or from the process if no enclosing activity specifies this attribute.
and that the "standard-elements" referred to above are:
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<targets>? <joinCondition expressionLanguage="anyURI"?>? ... bool-expr ... </joinCondition>
<target linkName="ncname" />+</targets><sources>?
<source linkName="ncname">+ <transitionCondition expressionLanguage="anyURI"?>? ... bool-expr ... </transitionCondition> </source></sources>
6.3. Language Extensibility
WS-BPEL contains constructs that are generally sufficient for expressing abstract and executable business processes. In some cases, however, it might be necessary to “extend” the WS-BPEL language with additional constructs from other XML namespaces.
WS-BPEL supports extensibility by allowing namespace-qualified attributes to appear on any WS-BPEL element and by allowing elements from other namespaces to appear within WS-BPEL defined elements. This is allowed in the XML Schema specifications for WS-BPEL.
If, during the processing of a WS-BPEL process an element or an
attribute of non-WS-BPEL namespace is encountered that is not
recognized by the processor then the element and its children MUST be treated
as if they were not present in the WS-BPEL
process instancedefinition.
The previously defined ignore semantics make it possible to add optional
attributes or elements to WS-BPEL that can be safely ignored if
not recognized. In the case of unsupported mandatory extensions (see section
13.7
“Extension Declarations”)
the previous logic is unnecessary as the entire process instance definition
will be rejected.
Extensions MUST NOT contradict the semantics of any element or attribute defined by the WS-BPEL specification. Extensions that affect the semantics of WS-BPEL processes MUST appear in the WS-BPEL process definition or its directly referenced WSDL portTypes, property alias definitions or property definitions.
Apart from core WS-BPEL process constructs, extensions are also allowed in WSDL-based WS-BPEL constructs, such as, <partnerLinkType>, <role>, <property> and <propertyAlias>. The same syntax pattern and semantic rules for extensions of core BPEL constructs are applied to these extensions as well. Particularly, <extension> directives of a WS-BPEL process are applied to all extensions used in WSDL-based WS-BPEL constructs, of which the WSDL definitions are transitively referenced by the process.
The optional <documentation>
construct is designed to be , an integral
part of Language Extensibility, is applicable to any WS-BPEL Extensible construct.
The content of <documentation> are for human-consumption. Example types
for those content are: plain text, HTML and XHTML. Tool-implementation specific
information (e.g. the graphical layout details) should be added through
elements and attributes of other namespaces, using the general WS-BPEL Language
Extensibility mechanism.
6.4. Document Linking
A WS-BPEL process definition relies on XML Schema and WSDL 1.1 for the definition of datatypes and service interfaces. Process definitions also rely on other constructs such as partner link types, variable properties and property aliases (defined later in this specification) which are defined within WSDL 1.1 documents using the WSDL 1.1 language extensibility feature.
The <import> element is used within a WS-BPEL
process to explicitly indicate a dependency on external XML Schema or WSDL
definitions. Any number of <import> elements may appear as initial
children of the <process> element, before any other child element. Each <import>
element contains three mandatory attributes
·namespace.
The namespace attribute specifies the URI namespace of the imported
definitions.
·location.
The location attribute contains a URI indicating the location of a document
that contains relevant definitions in the namespace specified. The document
located at the URI MUST contain definitions belonging to the same namespace as
indicated by the namespace attribute.
·importType.
The importType attribute identifies the type of document being imported by
providing the URI of the encoding language. The value MUST be set to "http://www.w3.org/2001/XMLSchema"
when importing XML Schema 1.0 documents, and to "http://schemas.xmlsoap.org/wsdl/"
when importing WSDL 1.1 documents.
The presence of an <import> element should be
interpreted as a hint to the WS-BPEL processor. In particular, processors are
not required to retrieve the imported document from the location specified on
the <import> element.The
<import> element is used within a WS-BPEL process to explicitly indicate
a dependency on external XML Schema or WSDL definitions. Any number of
<import> elements may appear as initial children of the <process>
element, before any other child element. Each <import> element contains a
mandatory and two optional attributes.
· “namespace”. The namespace attribute specifies an absolute URI that identifies the imported definitions. This attribute is optional. An import element without a namespace attribute indicates that external definitions are in use which are not namespace qualified.
· “location”. The location attribute contains a URI indicating the location of a document that contains relevant definitions in the namespace specified. The location URI may be a relative URI, following the usual rules for resolution of the URI base (XML Base and RFC 2396). The location attribute is optional. An import element without a location attribute indicates that external definitions are used by the process but makes no statement about where those definitions may be found. The document located at the location URI MUST identify the definitions it contains with a URI matching the URI indicated by the namespace attribute. The location attribute is a hint and that the BPEL Processor is not required to retrieve the document being imported from the specified location.
· “importType”. The importType attribute identifies the type of document being imported by providing an absolute URI that identifies the encoding language used in the document. The value of the importType attribute MUST be set to "http://www.w3.org/2001/XMLSchema"; when importing XML Schema 1.0 documents, and to "http://schemas.xmlsoap.org/wsdl/"; when importing WSDL 1.1 documents. Note: other importType URI values MAY be used here.
Observe that according to these rules, it is permissible to have an import element without namespace and location attributes, and only containing an importType attribute. Such an import element indicates that external definitions of the indicated type are in use which are not namespace qualified, and makes no statement about where those definitions may be found.
A BPEL process definition MUST import all XML Schema and WSDL definitions it uses. This includes all XML Schema type and element definitions, all WSLD port types and message types as well as property and property alias definitions used by the process. In order to support the use of definitions from namespaces spanning multiple documents, a BPEL process MAY include more than one import declarations for the same namespace and importType, provided that those declarations include different location values. Import elements are conceptually unordered. It is an error if the imported documents contain conflicting definitions of a component used by the importing process definition (as could be caused, for example, when the XSD redefinition mechanism is used).
Schema definitions defined in the types section of a WSDL document which is imported by a BPEL process definition are considered to be effectively imported themselves and are available to the process for the purpose of defining XML Schema variables. However, documents (or namespaces) imported by an imported document (or namespace) MUST NOT be transitively imported by the BPEL processor. In particular, this means that if an external item is used by a BPEL process, then a document (or namespace) that defines that item MUST be directly imported by the process; observe however that this requirement does not limit the ability of the imported document itself to import other documents or namespaces. The following example clarifies some of the issues related to the the lack of transitivity of imports.
Assume a document D1 define a type called a:Type. But a:Type's definition could depend on another type called b:Type which is defined in document D2. D1 could include an import for D2 thus making b:Type's definition available for use within the definition of a:Type. If a BPEL process refers to a:Type it must import document D1. By importing D1 the BPEL process can legally refer to a:Type. But the BPEL process could not refer to b:Type even though D1 imports D2. This is because transitivity of import is not supported by BPEL. Note, however, that D1 can still import D2 and a:Type can still use b:Type in its definition. In order to allow the BPEL process to refer to b:Type it would be necessary for the BPEL process to directly import document D2.
6.5 The Lifecycle of a Business Process
As noted in the introduction, the interaction model that is directly supported by WSDL is essentially a stateless client-server model of synchronous or uncorrelated asynchronous interactions. WS-BPEL, builds on WSDL by assuming that all external interactions of the business process occur through Web Service operations. However, WS-BPEL business processes represent stateful long-running interactions in which each interaction has a beginning, defined behavior during its lifetime, and an end. For example, in a supply chain, a seller's business process might offer a service that begins an interaction by accepting a purchase order through an input message, and then returns an acknowledgement to the buyer if the order can be fulfilled. It might later send further messages to the buyer, such as shipping notices and invoices. The seller's business process remembers the state of each such purchase order interaction separately from other similar interactions. This is necessary because a buyer might be carrying on many simultaneous purchase processes with the same seller. In short, a WS-BPEL business process definition can be thought of as a template for creating business process instances.
The creation of a process instance in WS-BPEL is always implicit; activities that receive messages (that is, receive activities and pick activities) can be annotated to indicate that the occurrence of that activity causes a new instance of the business process to be created. This is done by setting the createInstance attribute of such an activity to "yes". When a message is received by such an activity, an instance of the business process is created if it does not already exist (see Providing Web Service Operations and Pick).
To be instantiated, each business process must contain at least one such "start activity." That is, a receive/pick activity annotated with a createInstance="yes" attribute. See section 11.4 for more details on start activities.
If more than one start activity is enabled concurrently, then all such activities MUST share at least one common correlation set (see Correlation and the Multiple Start Activities example).
If a process contains exactly one start activity then the use of
correlation sets is unconstrained. This includes a pick with multiple onMessage branches; each such branch can use different correlation sets or no correlation sets.
A business process instance is terminated in one of the following ways:
· When the activity that defines the behavior of the process as a whole completes. In this case the termination is normal.
· When a fault reaches the process scope, and is either handled or not handled. In this case the termination is considered abnormal even if the fault is handled and the fault handler does not rethrow any fault. A compensation handler is never installed for a scope that terminates abnormally.
· When a process instance is explicitly terminated by an exit activity (see Terminating the Service Instance). In this case the termination is abnormal.
The structure of the main processing section is defined by the outer <sequence> element, which states that the three activities contained inside are performed in order. The customer request is received (<receive> element), then processed (inside a <flow> section that enables concurrent behavior), and a reply message with the final approval status of the request is sent back to the customer (<reply>). Note that the <receive> and <reply> elements are matched respectively to the <input> and <output> messages of the "sendPurchaseOrder" operation invoked by the customer, while the activities performed by the process between these elements represent the actions taken in response to the customer request, from the time the request is received to the time the response is sent back (reply).
A receive activity for an inbound request/response operation is said to be open if that activity has been performed and no corresponding reply activity has been performed. If the process instance reaches the end of its behavior, and one or more receive activities remain open, then the status of the instance becomes undefined. This condition indicates a modeling error that was not detected by static analysis.
The example makes the implicit assumption that the customer request can be processed in a reasonable amount of time, justifying the requirement that the invoker wait for a synchronous response (because this service is offered as a request-response operation). When that assumption does not hold, the interaction with the customer is better modeled as a pair of asynchronous message exchanges. In that case, the "sendPurchaseOrder" operation is a one-way operation and the asynchronous response is sent by invoking a second one-way operation on a customer "callback" interface. In addition to changing the signature of "sendPurchaseOrder" and defining a new portType to represent the customer callback interface, two modifications need to be made in the preceding example to support an asynchronous response to the customer. First, the partner link type "purchasingLT" that represents the process-customer connection needs to include a second role ("customer") listing the customer callback portType. Second, the <reply> activity in the process needs to be replaced by an <invoke> on the customer callback operation.
The processing taking place inside the <flow> element consists of three <sequence> blocks running concurrently. The synchronization dependencies between activities in the three concurrent sequences are expressed by using "links" to connect them. The links are defined inside the flow and are used to connect a source activity to a target activity. (Note that each activity declares itself as the source or target of a link by using the nested <source> and <target> elements.) In the absence of links, the activities nested directly inside a flow proceed concurrently. In the example, however, the presence of two links introduces control dependencies between the activities performed inside each sequence. For example, while the price calculation can be started immediately after the request is received, shipping price can only be added to the invoice after the shipper information has been obtained; this dependency is represented by the link (named "ship-to-invoice") that connects the first call on the shipping provider ("requestShipping") with sending shipping information to the price calculation service ("sendShippingPrice"). Likewise, shipping scheduling information can only be sent to the manufacturing scheduling service after it has been received from the shipper service; thus the need for the second link ("ship-to-scheduling").
Observe that information is passed between the different activities in an implicit way through the sharing of globally visible data variables. In this example, the control dependencies represented by links are related to corresponding data dependencies, in one case on the availability of the shipper rates and in another on the availability of a shipping schedule. The information is passed from the activity that generates it to the activity that uses it by means of two global data variables ("shippingInfo" and "shippingSchedule").
Certain operations can return faults, as defined in their WSDL definitions. For simplicity, it is assumed here that the two operations return the same fault ("cannotCompleteOrder"). When a fault occurs, normal processing is terminated and control is transferred to the corresponding fault handler, as defined in the <faultHandlers> section. In this example the handler uses a <reply> element to return a fault to the customer (note the "faultName" attribute in the <reply> element).
Finally, it is important to observe how an assignment activity is used to transfer information between data variables. The simple assignments shown in this example transfer a message part from a source variable to a message part in a target variable, but more complex forms of assignments are also possible.
7. Partner Link Types, Partner Links, and Endpoint References
A very important, if not the most important, use case for WS-BPEL will be in describing cross-enterprise business interactions in which the business processes of each enterprise interact through Web Service interfaces with the processes of other enterprises. An important requirement for realistic modeling of business processing in this environment is the ability to model the required relationship with a partner process. WSDL already describes the functionality of a service provided by a partner, at both the abstract and concrete levels. The relationship of a business process to a partner is typically peer-to-peer, requiring a two-way dependency at the service level. In other words, a partner represents both a consumer of a service provided by the business process and a provider of a service to the business process. This is especially the case when the interactions are based on asynchronous messaging rather than on remote procedure calls. The notion of Partner links is used to directly model peer-to-peer conversational partner relationships. Partner links define the shape of a relationship with a partner by defining the message and port types used in the interactions in both directions. However, the actual partner service may be dynamically determined within the process. WS-BPEL uses a notion of endpoint reference, manifested as a service reference container (“bpws:service-ref”), to represent the dynamic data required to describe a partner service endpoint.
It is important to emphasize that the notions of partner link and endpoint reference used here are preliminary. The specification for these concepts as they relate to Web Services is still evolving, and we expect normative definitions for them to emerge in future. The WS-BPEL specification will be updated to conform to the expected future standards.
7.1. Partner Link Types
A partner link type characterizes the conversational relationship between two services by defining the "roles" played by each of the services in the conversation and specifying the portType provided by each service to receive messages within the context of the conversation. The following example illustrates the basic syntax of a partner link type declaration:
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<partnerLinkType name="BuyerSellerLink"
xmlns="http://schemas.xmlsoap.org/ws/2004/03/partner-link/">
<role name="Buyer" portType="buy:BuyerPortType"/>
<role name="Seller" portType="sell:SellerPortType"/>
</partnerLinkType>
Each role specifies exactly one WSDL portType.
In the common case, portTypes of the two roles originate from separate namespaces. However, in some cases, both roles of a partner link type can be defined in terms of portTypes from the same namespace. The latter situation occurs for partner link types that define "callback" relationships between services.
The partner link type definition can be a separate artifact independent of either service's WSDL document. Alternatively, the partner link type definition can be placed within the WSDL document defining the portTypes from which the different roles are defined.
The extensibility mechanism of WSDL 1.1 is used to define partnerLinkType as a new definition type to be placed as an immediate child element of a <wsdl:definitions> element in all cases. This allows reuse of the WSDL target namespace specification and, more importantly, its import mechanism to import portTypes. For cases where a partnerLinkType declaration is linking the portTypes of two different services, the partnerLinkType declaration can be placed in a separate WSDL document (with its own targetNamespace).
The syntax for defining a partnerLinkType is:
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<definitions name="ncname" targetNamespace="uri"
xmlns="http://schemas.xmlsoap.org/wsdl/">
...
<plnk:partnerLinkType name="ncname">
<plnk:role name="ncname" portType="qname"/>
<plnk:role name="ncname" portType="qname"/>?
</plnk:partnerLinkType>
...
</definitions>
This defines a partner link type in the namespace indicated by the value of the "targetNamespace" attribute of the WSDL document element. The portTypes identified within roles are referenced by using QNames as for all top-level WSDL definitions.
Note that in some cases it can be meaningful to define a partner link type containing exactly one role instead of two. That defines a partner linking scenario where one service expresses a willingness to link with any other service, without placing any requirements on the other service.
Examples of partnerLinkType declarations are found in various business process examples in this specification.
7.2. Partner Links
The services with which a business process interacts are modeled as partner links in WS-BPEL. Each partner link is characterized by a partnerLinkType. More than one partner link can be characterized by the same partnerLinkType. For example, a certain procurement process might use more than one vendor for its transactions, but might use the same partnerLinkType for all vendors.
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<partnerLinks>
<partnerLink name="ncname" partnerLinkType="qname"
myRole="ncname"? partnerRole="ncname"? initializePartnerRole="yes|no"?>+
</partnerLink>
</partnerLinks>
Each partnerLink is named, and this name is used for all service interactions via that partnerLink. This is critical, for example, in correlating responses to different partnerLinks for simultaneous requests of the same kind (see Invoking Web Service Operations and Providing Web Service Operations).
The role of the business process itself is indicated by the attribute myRole and the role of the partner is indicated by the attribute partnerRole. In the degenerate case where a partnerLinkType has only one role, one of these attributes is omitted as appropriate.
Note that the partnerLink declarations specify the shape of the relationships that the WS-BPEL process will employ in its behavior. Before operations on a partner's service can be invoked via a partnerLink, the binding and communication data for the partner service must be available. The relevant information about a partner service can be set as part of business process deployment. This is outside the scope of WS-BPEL. However, it is also possible to select and assign actual partner services dynamically, and WS-BPEL provides the mechanisms to do so via assignment of endpoint references. In fact, because the partners are likely to be stateful, the service endpoint information needs to be extended with instance-specific information. WS-BPEL allows the endpoint references implicitly present in partnerLinks to be both extracted and assigned dynamically, and also to be set more than once. See Assignment for the mechanisms used for dynamic assignment of endpoint references to partner services.
The initializePartnerRole attribute specifies if the BPEL processor is required to initialize a partnerLink's partnerRole value. The attribute has no affect on the partnerRole's value after its initialization. The initializePartnerRole attribute MUST NOT be used on a partnerLink that does not have a partner role; this restriction MUST be statically enforced. If the initializePartnerRole attribute is set to "yes" then the BPEL processor MUST initialize the EPR for the specified partnerLink/partnerRole combination before that partnerRole is first referenced by the BPEL process. If the initializePartnerRole attribute is set to "no" then the BPEL processor MUST NOT initialize the EPR for the specified partnerLink/partnerRole combination before that partnerRole is first referenced by the BPEL process. If the initializePartnerRole attribute is omitted then its value MUST be treated as "no".
A partnerLink can be declared within a process or scope element. The name of a partnerLink should be unique amongst the names of all partnerLinks defined within the same immediately enclosing scope. This requirement MUST be statically enforced.. Access to partnerLink follows common lexical scoping rules, similar to the rules for variables. A partnerLink resolves to the nearest enclosing scope, regardless of the type of the partnerLink. If a local partnerLink declared in an enclosing scope, the local partnerLink will be used in local assignments and message sending/receiving activities. The lifecyle of a partnerLink is same as the lifecycle of the scope declaring the partnerLink. The initial binding information of a partnerLink can be set as a part of business process deployment, regardless whether it is declared on the process or scope element level.
7.4. Endpoint References
WSDL makes an important distinction between portTypes and ports. PortTypes define abstract functionality by using abstract messages. Ports provide actual access information, including communication service endpoints and (by using extension elements) other deployment related information such as public keys for encryption. Bindings provide the glue between the two. While the user of a service must be statically dependent on the abstract interface defined by portTypes, some of the information contained in port definitions can typically be discovered and used dynamically.
The fundamental use of endpoint references is to serve as the mechanism for dynamic communication of port-specific data for services. An endpoint reference makes it possible in WS-BPEL to dynamically select a provider for a particular type of service and to invoke their operations. WS-BPEL provides a general mechanism for correlating messages to stateful instances of a service, and therefore endpoint references that carry instance-neutral port information are often sufficient. However, in general it is necessary to carry additional instance-identification tokens in the endpoint reference itself.
Every partner role in a partnerLink in a WS-BPEL process instance is assigned a unique endpoint reference in the course of the deployment of the process or dynamically by an activity within the process.
Endpoint references associated with parterRole and myRole of partnerLinks are manifested as service reference containers (“bpws:service-ref”). This container is used as envelope to wrap around the actual endpoint reference value, when a WS-BPEL process interacts the endpoint reference of a partnerLink. It provides pluggability of different versions of service endpoint referencing schemes being used within a BPEL program. The design pattern here is similar to those of expression language, also known as open-content models.
The “bpws:service-ref” has an optional attribute called “reference-scheme” to to denote the URI of the reference interpretation scheme of service endpoint, which is the child element of bpws:service-ref.
Most likely, the URI of reference scheme and the namespace URI of the child element of bpws:service-ref are not necessarily the same. Typically, this optional attribute is used ONLY when the child element of the “bpws:service-ref” is ambiguous by itself. The optional attribute supplies further information to disambiguate the usage of the content. One example would be: different treatments of wsdl:service element, if wsdl:service is used as the endpoint reference.
If that attribute is not specified, use the namespace URI of the content element within the wrapper to determine the reference scheme of service endpoint.
If the attribute is specified, use the URI as the reference scheme of service endpoint and treat the content element within the wrapper accordingly. When the "reference-scheme" attribute is specified, the URI value is most likely different from the namespace URI of the content element for EPR.
When the BPEL container fails to interpret the combination of the "reference-scheme" attribute and the content element OR just the content element alone, a standard fault "bpws:unsupportedReference" must be thrown.
When WS-BPEL users interact and manipulate endpoint references of partnerLinks, The “bpws:service-ref” element are NOT exposed to WS-BPEL users in all cases. For example, when people try to do an assignment from the endpoint reference of myRole of partnerLink-A to that of partnerRole of partner-B. On the contrary, if people try to do assignment from a messageType or element based variable through expression or from a service-ref -form of from-spec, the “bpws:service-ref” is visible to WS-BPEL users.
8. Variable Properties
8.1. Motivation
8.1.1 Motivation for Message Properties
The data in a message consists conceptually of two parts: application data and protocol relevant data, where the protocols can be business protocols or infrastructure protocols providing higher quality of service. An example of business protocol data is the correlation tokens that are used in correlation sets (see Correlation). Examples of infrastructure protocols are security, transaction, and reliable messaging protocols. The business protocol data is usually found embedded in the application-visible message parts, whereas the infrastructure protocols almost always add implicit extra parts to the message types to represent protocol headers that are separate from application data. Such implicit parts are often called message context because they relate to security context, transaction context, and other similar middleware context of the interaction. Business processes might need to gain access to and manipulate both kinds of protocol-relevant data. The notion of message properties is defined as a general way of naming and representing distinguished data elements within a message, whether in application-visible data or in message context. For a full accounting of the service description aspects of infrastructure protocols, it is necessary to define notions of service policies, endpoint properties, and message context. This work is outside the scope of
WS-BPEL. Message properties are defined here in a sufficiently general way to cover message context consisting of implicit parts, but the use in this specification focuses on properties embedded in application-visible data that is used in the definition of business protocols and abstract business processes.
8.1.2 Motivation for Variable Properties
Message properties are an instance of a more generic mechanism, variable properties. All variables in BPEL can have properties defined on them. Properties are useful on non-message variables as a way to isolate the BPEL process’s logic from the details of a particular variable’s definition. Using properties a BPEL process can isolate its variable initialization logic in one place and then set and get properties on that variable in order to manipulate it. If the variable’s definition is later changed the bulk of the BPEL process definition that manipulates that variable can remain unchanged.
8.2. Defining Properties
A property definition creates a globally unique name and associates it with an XML Schema type. The intent is not to create a new type. The intent is to create a name that has greater significance than the type itself. For example, a sequence number can be an integer, but the integer type does not convey this significance, whereas a globally named sequence-number property does. Properties can occur anywhere in a variable.
A typical use for a property in WS-BPEL is to name a token for correlation of service instances with messages. For performance reasons, properties used for correlation MUST be defined using XML Schema simple types, this restriction MUST be statically enforced. For example, a social security number might be used to identify an individual taxpayer in a long-running multiparty business process regarding a tax matter. A social security number can appear in many different message types, but in the context of a tax-related process it has a specific significance as a taxpayer ID. Therefore a global name is given to this use of the type by defining a property, as in the following example:
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<definitions name="properties"
targetNamespace="http://example.com/properties.wsdl"
xmlns:tns="http://example.com/properties.wsdl"
xmlns:txtyp="http://example.com/taxTypes.xsd"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<! -- import schema taxTypes.xsd -- > <!-- define a correlation property -->
<bpws:property name="taxpayerNumber"
type="txtyp:SSN"/>
...
</wsdl:definitions>
In correlation, the property name must have global significance to be of any use. Properties such as price, risk, response latency, and so on, which are used in conditional behavior in a business process, have similar global and public significance. It is likely that they will be mapped to multiple messages, and therefore they need to be globally named as in the case of correlation properties. Such properties are essential, especially in abstract processes.
Even in the general case of properties on XML typed WS-BPEL variables the property name should maintain its generic nature. The name is intended to identify a certain kind of value, often with an implied semantic. Any variable the property is available on is therefore expected to provide a value that meets not just the syntax of the property definition but also its semantics.
The WSDL extensibility mechanism is used to define properties so that the target namespace and other useful aspects of WSDL are available.
The WS-BPEL standard namespace, "http//schemas.xmlsoap.org/ws/2004/03/business-process/", is used for property definitions. The syntax for a property definition is a new kind of WSDL definition as follows:
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<wsdl:definitions name="ncname">
<bpws:property name="ncname" type="qname"? element="qname"?/>
...
</wsdl:definitions>
Either the type or element attributes MUST be present but not both. Properties used in business protocols are typically embedded in application-visible message data. The notion of aliasing is introduced to map a global property to a field in a specific message part or a value in a XML variable. The property name becomes an alias for the message part and location or XML variable value, and can be used as such in Expressions and Assignment in abstract business processes. As an example, consider the following WSDL message definition:
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<definitions name="messages"
targetNamespace="http://example.com/taxMessages.wsdl"
xmlns:txtyp="http://example.com/taxTypes.xsd"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define a WSDL application message --> <message name="taxpayerInfo"> <part name="identification" element="txtyp:socialsecnumber"/> </message> ...</definitions>
The definition of a global property and its location in a particular field of the message are shown in the next WSDL fragment:
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<definitions name="properties"
targetNamespace="http://example.com/properties.wsdl"
xmlns:tns="http://example.com/properties.wsdl"
xmlns:txtyp="http://example.com/taxTypes.xsd"
xmlns:txmsg="http://example.com/taxMessages.wsdl"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define a correlation property -->
<bpws:property name="taxpayerNumber" type="txtyp:SSN"/>
...
<bpws:propertyAlias propertyName="tns:taxpayerNumber"
messageType="txmsg:taxpayerInfo" part="identification">
<query> /txtyp:socialsecnumber </query>
</bpws:propertyAlias>
</definitions>
The bpws:propertyAlias defines a globally named property tns:taxpayerNumber as an alias for a location in the identification part of the message type txmsg:taxpayerInfo.
The syntax for a propertyAlias definition is:
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<definitions name="ncname"
...
>
<bpws:propertyAlias propertyName="qname"
messageType="qname"? part="ncname"?
type="qname"? element="qname"?> <query queryLanguage="anyURI"?>? ... queryString ... </query> </bpws:propertyAlias>
...
</wsdl:definitions>
The interpretation of the message and part attributes, as well as the <query> element is the same as in the corresponding from-spec in copy assignments (see Assignment).
8.3 Defining Property Aliases
Properties used in business protocols are typically embedded in application-visible variables. The notion of aliasing is introduced to map a global property to a field in a specific message part or variable value. The property name becomes an alias for the message part and/or location, and can be used as such in Expressions and Assignment in abstract business processes. As an example, consider the following WSDL message definition:
<definitions name="messages"
targetNamespace="http://example.com/taxMessages.wsdl"
xmlns:txtyp="http://example.com/taxTypes.xsd"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define a WSDL application message -->
<message
name="taxpayerInfoMsg">
<part name="identification"
element="txtyp:taxPayerInfoElem"/>
</message>
...
</definitions>
The definition of a global property and its location in a particular field of the message are shown in the next WSDL fragment:
<definitions name="properties"
targetNamespace="http://example.com/properties.wsdl"
xmlns:tns="http://example.com/properties.wsdl"
xmlns:txtyp="http://example.com/taxTypes.xsd"
xmlns:txmsg="http://example.com/taxMessages.wsdl"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define a correlation property -->
<bpws:property name="taxpayerNumber"
type="txtyp:SSN"/>
...
<bpws:propertyAlias
propertyName="tns:taxpayerNumber" messageType="txmsg:taxpayerInfoMsg"
part="identification">
<query>
txtyp:socialsecnumber
</query>
</bpws:propertyAlias>
<bpws:propertyAlias propertyName="tns:taxpayerNumber"
element="txtyp:taxPayerInfoElem">
<query>
txtyp:socialsecnumber
</query>
</bpws:propertyAlias>
</definitions>
The first bpws:propertyAlias defines a globally named property tns:taxpayerNumber as an alias for a location in the identification part of the message type txmsg:taxpayerInfo.
The second bpws:propertyAlias provides a second definition for the same globally named property tns:taxpayerNumber but this time as an alias for a location inside of the element txtyp:taxPayerInfoElem.
The presence of both aliases means that it is possible to retrieve the social security number from both a variable holding a message of messageType txmsg:taxpayerInfo as well as an element defined using txtyp:taxPayerInfoElem.
The syntax for a propertyAlias definition is:
<definitions name="ncname"
... >
<bpws:propertyAlias propertyName="qname"
messageType="qname"? part="ncname"?
type="qname"? element="qname"?>
<query queryLanguage="anyURI"?>?
... queryString ...
</query>
</bpws:propertyAlias>
...
</wsdl:definitions>
A property alias element MUST use one of the three following combinations of
attributes:
· messageType and part,
· type or
· element.
When a propertyAlias is used with the messageType/part
combination then the property MUST be available on all BPEL variables where the
qname value used in the messageType attribute on the declaration of both the
variable and the propertyAlias are identical. The part attribute and query
element is applied against the BPEL messageType variable to either set or get
the property variable in the same way that the part attribute and query element
are used in the first from and to specs in copy assignments.
Using the same “tns:taxpayerNumber”
example from above, for a message variable “myTaxPayerInfoMsg” of type “txmsg:taxpayerInfo”:
<from variable="myTaxPayerInfoMsg" property="tns:taxpayerNumber" />
and
<from>$myTaxPayerInfoMsg.identification/txtyp:socialsecnumber</from>
have the same output. Please see Assignment for details.
If a propertyAlias is used with a type attribute then the property MUST be available on all BPEL variables where the qname value used in the type attribute on the declaration of both the variable and the propertyAlias are identical. The query is applied against the BPEL variable to either set or get the property variable in the same way that the query is used in the first from and to specs in copy assignments when applied against BPEL variables defined using a type.
If a propertyAlias is used with an element attribute then the property MUST be available on all BPEL variables where the qname value used in the element attribute on the declaration of both the variable and the propertyAlias are identical. The query is applied against the BPEL variable to either set or get the property variable in the same way that the query is used in the first from and to specs in copy assignments when applied against BPEL variables defined using an element definition.
A BPEL process MUST NOT be accepted for processing if it defines two or more propertyAlias’s for the same property name and BPEL variable type. For example, it is not legal to define two propertyAlias’s for the property taxpayernumber and the messageType txmsg:taxpayerInfoMsg. The same logic would prohibit having two propertyAliases on the same element qname and property name value or two propertyAliases on the same type qname and property name value.
9. Data Handling
Business processes model stateful interactions. The state involved consists of messages received and sent as well as other relevant data such as time-out values. The maintenance of the state of a business process requires the use of state variables, which are called variables in WS-BPEL. Furthermore, the data from the state needs to be extracted and combined in interesting ways to control the behavior of the process, which requires data expressions. Finally, state update requires a notion of assignment. WS-BPEL provides these features for XML data types and WSDL message types. The XML family of standards in these areas is still evolving, and using the process-level attributes for query and expression languages provides for the incorporation of future standards.
Executable processes are permitted to use the full power of data selection and assignment but are not permitted to use opaque values. Abstract processes, on the other hand, are permitted to hide behavior. Detailed differences are specified in the following sections.The extensions required for abstract and executable processes are concentrated in the datahandling feature set. Executable processes are permitted to use the full power of data selection and assignment but are not permitted to use nondeterministic values. Abstract processes are restricted to limited manipulation of values contained in variable properties but are permitted to use nondeterministic values to reflect the consequences of hidden private behavior. Detailed differences are specified in the following sections.
9.3. Expressions
(Editor note: re-arranging the order of this section later for
ease of tracking for this version)
WS-BPEL uses several types of expressions. The kinds of expressions used are as
follows (relevant usage contexts are listed in parentheses):
· Boolean-valued expressions (transition conditions, join conditions, while condition, and if conditions)
· Deadline-valued expressions ("until" expression of onAlarm and wait)
· Duration-valued expressions ("for" expression of onAlarm and wait, "repeatEvery" expression of onAlarm)
· General expressions (assignment)
WS-BPEL provides an extensible mechanism for the language used in these expressions. The language is specified by the expressionLanguage attribute of the process element. In addition, language constructs that require or allow conditional expressions (such as “if”, “while” and others) provide the ability to override the default expression language for individual expressions. Compliant implementations of the current version of WS-BPEL MUST support the use of XPath 1.0 as the expression language. XPath 1.0 is indicated by the default value of the expressionLanguage attribute, which is:
urn:oasis:names:tc:wsbpel:2.0:sublang:xpath1.0
which represents the usage of XPath 1.0 within WS-BPEL 2.0. The URI of the
corresponding XPath 1.0 specification is:
http://www.w3.org/TR/1999/REC-xpath-19991116
Given an expression language, it must be possible to query data from variables, to extract property values, and to query the status of links from within expressions. This specification defines those functions for XPath 1.0 only, and it is expected that other expressionlanguage bindings will provide equivalent functionality. The rest of this section is specific to XPath 1.0.
WS-BPEL introduces several extension functions to XPath's built-in functions to enable XPath 1.0 expressions to access information from the process. The extensions are defined in the standard WS-BPEL namespace http://schemas.xmlsoap.org/ws/2004/03/businessprocess/. The prefix "bpws:" is associated with this namespace.
Any qualified names used within XPath expressions are resolved by using namespace declarations currently in scope in the WS-BPEL document at the location of the expression.
The arguments to all XPath functions defined in this specification MUST be given as quoted strings. The previous requirement MUST be statically enforced. It is therefore illegal to pass into a BPEL XPath function any XPath variables, the output of XPath functions, a XPath location path or any other value that is not a quoted string. This means, for example, that getVariableProperty("varA","propB") meets the previous requirement while getVariableProperty( $varA, string(getVariableProperty("varB","propB") ) does not. Note that the previous requirement institutes a restriction which does not exist in the XPath standard.
The following functions are defined by this specification:
bpws:getVariableProperty ('variableName', 'propertyName')
This function extracts global property values from variables.
The first argument names the source variable for the data and the second is the
qualified name (QName) of the global property to select from that variable (see
Variable Properties). If the referenced property is not defined or if
there does not exist a propertyAlias to associate the property with the
referenced variable then the semantics of the process is undefined. The return value of this function is calculated by applying the
appropriate propertyAlias for the requested property to the current value of
the submitted variable. If the application of the XPATH in the propertyAlias to
the variable value results in a response that contains anything other than
exactly one information item and/or a collection of Character information items
then a bpws:selectionFailure fault MUST be thrown.
These WS-BPEL-defined extension functions are available for use within all
XPath 1.0 expressions.
The syntax of XPath 1.0 expressions for WS-BPEL is considered in the following paragraphs.
9.3.1. Boolean Expressions
These are expressions that conform to the XPath 1.0 Expr production where the evaluation results in Boolean values.
9.3.2. Deadline-Valued Expressions
These are expressions that conform to the XPath 1.0 Expr production where the evaluation results in values that are of the XML Schema types dateTime or date. Note that XPath 1.0 is not XML Schema aware. As such, none of the built-in functions of XPath 1.0 are capable of producing or manipulating dateTime or date values. However, it is possible to write a constant (literal) that conforms to XML Schema definitions and use that as a deadline value or to extract a field from a variable (part) of one of these types and use that as a deadline value. XPath 1.0 will treat that literal as a string literal, but the result can be interpreted as a lexical representation of a dateTime or date value.
9.3.3. Duration-Valued Expressions
These are expressions that conform to the XPath 1.0 Expr production where the evaluation results in values that are of the XML Schema type duration. The preceding discussion about XPath 1.0's XML Schema unawareness applies here as well.
9.3.4. General Expressions
These are expressions that conform to the XPath 1.0 Expr production where the evaluation results in any XPath value type (string, number, or Boolean).
If the execution of an expression results in an unhandled expression language execution fault, then the WS-BPEL standard fault bpws:subLanguageExecutionFault MUST be thrown.
9.1. Variables
(Editor note: re-arranging the order of this section later for
ease of tracking for this version)
Business processes specify stateful interactions involving the exchange of
messages between partners. The state of a business process includes the
messages that are exchanged as well as intermediate data used in business logic
and in composing messages sent to partners.
Variables provide the means for holding messages that constitute the state of a business process. The messages held are often those that have been received from partners or are to be sent to partners. Variables can also hold data that are needed for holding state related to the process and never exchanged with partners.
The type of each variable may be a WSDL message type, an XML Schema type (simple or complex) or an XML Schema element. The syntax of the variables declaration is:
<variables>
<variable name="ncname" messageType="qname"?
type=”qname”? element=”qname”?/>+ from-spec?
</variables>
The name of a variable MUST be unique amongst the names of all variables defined within the same immediately enclosing scope. This requirement MUST be statically enforced.. Variable names are NCNames (as defined in XML Schema specification) but in addition they MUST NOT contain the “.” character. This restriction is necessary because the “.” character is used as a delimiter in variable names in BPEL's default binding to XPath 1.0 (i.e. the binding identified by "urn:oasis:names:tc:wsbpel:2.0:sublang:xpath1.0"). The delimiter separates the WS-BPEL message type variable name and the name of one of its WSDL message parts. The concatenation of the WSDL message variable name, the delimiter and the WSDL part name is used as an XPath variable reference which manifests the XML Infoset of the corresponding WSDL message part. Variable access follows common lexical scoping rules. A variable resolves to the nearest enclosing scope, regardless of the type of the variable. If a local variable has the same name as a variable defined in an enclosing scope, the local variable will be used in local assignments and/or getVariableProperty functions.
The messageType, type or element attributes are used to specify the type of a variable. Exactly one of these attributes must be used. Attribute messageType refers to a WSDL message type definition. Attribute type refers to an XML Schema type (simple or complex). Attribute element refers to an XML Schema element.
Using [Infoset] terminology, the infoset for a BPEL element variable consists of a document information item (DII) that contains exactly one child, an element information item (EII) which is pointed at by the document element property. The EII is the value of the element variable.
If a BPEL implementation chooses to manifest a simpleType variable as an XML infoset, the infoset should consist of a DII that contains exactly one child, an EII which is pointed at by the document element property. The properties of the document element, specifically the namespace name and local name properties, are undefined by this specification, as such an implementation MUST specify whatever namespace name/local name values it likes. However the children of the document element MUST exclusively consist of a series of character information items (CharIIs) that represent the simpleType value.A BPEL implementation MAY choose to map simpleType variables to non-XML-infoset data-models defined in the expression/query language being used. (e.g. Boolean in XPath 1.0)
A variable can optionally be initialized by using an in-line from-spec. From-spec is defined in section 9.3. Conceptually the in-line variable initializations are modeled as a virtual sequence activity that contains a series of virtual assign activities, one for each variable being initialized in the order they are listed in the variable declarations. The virtual assigns then each contain a single virtual copy whose from-spec is as given in the variable initialization and the to-spec points to the variable being created. The previous discussion of virtual sequences and assigns is only meant for modeling purposes. The description is strictly intended to describe initialization behavior in terms of previously understood concepts but there is no intention that the behavior be seen as actually implying that any of the 'virtual' sequences or assigns exist as anything other than a model of the expected behavior.
Variable initialization logic contained in scopes that contain or whose progeny contain a start activity MUST only use idempotent functions. The use of idempotent functions allows for all the values for such variables to be pre-computed and re-used on each process instance.
The infoset for a complexType variable consists of a document information item that contains exactly one child, an element information item which is pointed at by the document element property. The properties of the document element, specifically the namespace name and local name properties, are undefined by this specification, as such an implementation MUST specify whatever legal property values it likes. However the children of the document element MUST exclusively consist of the complexType values assigned to the variable. In order to simplify data access, WSDL parts of WSDL message variables are manifested in BPEL as infosets, one infoset per WSDL message part. BPEL engines MUST follow the following algorithm when manifesting a WSDL message part as an infoset.
For each part in the WSDL message definition:
Step 1 – Create a synthetic DII which has no children other than as specified below.
Step 2a – If the WSDL message part is defined using the type attribute then create an EII as a child of the document element. The local name and namespace name of the newly created EII are determined by the WS-BPEL 2.0 engine and are not specified by this document. The handling of this EII is similar to how WS-BPEL 2.0 handles the containers for complex and simple type XML variables. The contents of the new EII are required to conform to the contents defined by the referenced type definition.
Step 2b – If the WSDL message part is defined using the element attribute then create an EII as a child of the document element which manifests the element defined by the referenced type definition.
The previous models are conceptual; they define how WS-BPEL 2.0 submits and retrieves XML variable values using infoset definitions. But these models are not intended to require that WS-BPEL 2.0 implementations actually implement an infoset model, only that however variable binding is handled the end result duplicates the behaviors defined using the infoset model. For example, a WS-BPEL 2.0 implementation may choose to bind a simple type BPEL variable of type xs:string directly to a String object in XPath 1.0. The choice of mapping MUST be consistently applied to variables and WSDL message part values of the same XML schema type. E.g. if a xs:string variable is manifested as a string object, a xs:string message part MUST be manifested as a string object also. For detailed definition of manifestation of BPEL variables in XPath 1.0, please see “Binding BPEL Variables In XPath 1.0” section.
In summary, a BPEL variable is manifested as XML Infoset items in one of the following ways:
(1) a single XML infoset item: e.g. an element or complexType variable or a WSDL message part
(2) a sequence of Character Information Items for simple type data: e.g. used to manifest string (Please note these items may be manifested as a non XML infoset item when needed. e.g. Boolean)
An example of a variable declaration using a message type declared in a WSDL document with the targetNamespace "http://example.com/orders":
<variable xmlns:ORD="http://example.com/orders"
name="orderDetails" messageType="ORD:orderDetails"/>
Variables associated with message types can be specified as input or output variables for invoke, receive, and reply activities (see Invoking Web Service Operations and Providing Web Service Operations). When an invoke operation returns a fault message, this causes a fault in the current scope. The fault variable in the corresponding fault handler is initialized with the fault message received (see Scopes and Fault Handlers).
Each variable is declared within a scope and is said to belong to that scope. Variables that belong to the global process scope are called global variables. Variables may also belong to other, non-global scopes, and such variables are called local variables. Each variable is visible only in the scope in which it is defined and in all scopes nested within the scope it belongs to. Thus, global variables are visible throughout the process. It is possible to "hide" a variable in an outer scope by declaring a variable with an identical name in an inner scope. These rules are exactly analogous to those in programming languages with lexical scoping of variables.
A global variable is in an uninitialized state at the beginning of a process. A local variable is in an uninitialized state at the start of the scope it belongs to. Note that non-global scopes in general start and complete their behavior more than once in the lifetime of the process instance they belong to. Variables can be initialized by a variety of means including assignment and receiving a message. Variables can be partially initialized with property assignment or when some but not all parts in the message type of the variable are assigned values.
Values stored in variables can be
mutated during the course of process execution. The validate activity can be
used explicitly to ensure that values of variables are valid against their
associated XML data definition, including XML Schema simple type, complex type,
element definition and XML definitions of WSDL parts. The validate activity has a variables attribute, listings
the variables to validate. The attribute accepts one or more variable names
(NCNames), separated by whitespaces.which has a
NCNAMES value. The variables attribute points to the variables being validated. The syntax of the validate activity is:
<validate variables="ncnames-list" standard-attributes>
standard-elements
</validate>/>
When one or more variables are invalid against their correponding XML definition, a standard fault of "bpws:invalidVariables" fault MUST be thrown.
A BPEL implementation MAY provide a mechanism to turn on/off any explicit validation. E.g. validate activity.
An BPEL implementation MAY provide a configurable mechanism to enable or disable schema validation of incoming and outgoing messages during the execution of Web Service related activities, e.g., receive, reply, pick, onEvent and invoke activities. The details of configuration mechanism is out of the scope of this specification.
9.2 Usage of Query and Expression Languages
This section models the interaction between Query/Expression languages and the BPEL process from two different perspectives. The first perspective is BPEL's view of the query/expression languages. That view is restricted to what information BPEL will make available for use by the Query/Expression language. The second perspective is the Query/Expression language's view of BPEL, specifically XPath 1.0 and how XPath 1.0's execution context is initialized by BPEL.
9.2.1 Enclosing Elements
In order to describe the view that BPEL provides to Query/Expression languages it is necessary to introduce a new term - Enclosing Element.
Definition of an Enclosing Element of a Query or Expression language: Whenever
a query or expression language is used in BPEL (e.g. XPath 1.0), the Enclosing
Element is defined as the parent element in the BPEL process definition that
contains the Query or Expression. For example, in the following from
specification example:
<process>
...
<from>$myVar/abc/def</from>
...
</process>
The "from" element is the Enclosing Element.
The in-scope namespaces of the enclosing element are the namespaces visible to the Query/Expression language. (Note: XPath 1.0 does not have default namespace concept.)
The links, variables, partnerLinks, fault handlers, compensation handlers, etc. that are visible to a Query/Expression language are defined based on the visibility of those entities to the activity that the enclosing element is contained within. There is no requirement that a Query/Expression language must manifest all the different objects previously described, only that if such objects are accessible within the Query/Expression language then only the objects in scope to the enclosing element’s enclosing activity SHOULD be visible from within the Query/Expression language.
Evaluation of a BPEL expression or query will yield one of the following: (here we use XPath 1.0 expressions as examples)
(1) a single XML infoset item: e.g. $myFooVar/lines/line[2]
(2) a collection of XML infoset items e.g. $myFooVar/lines
(3) a sequence of
Character Information Items for simple type data
e.g. $myFooVar/lines/line[2]/text()
(Please note this sequence of items may be manifested as a non XML infoset item
when needed. e.g. boolean)
(4) a variable reference: e.g. <from>$myFooVar</from> <to>$myBarVar</to>
9.2.2 Binding BPEL Variables In XPath 1.0
With the exception of Link expressions whose variable access syntax and semantics are described in section 9.2.4, BPEL variables are accessible in XPath expressions in BPEL processes via XPath 1.0 variable bindings. Specifically, all BPEL variables visible from the enclosing element of an XPath 1.0 expression MUST be made available to the XPath 1.0 processor by manifesting the BPEL variable as an XPath variable binding whose name is the same as the BPEL variable's name, except the case of WSDL message variables declared with a messageType, which requires some special handling (discussed below).
BPEL variables declared using an element are manifested as a node-set XPath variable with a single member node. That node is a synthetic DII that contains a single child, the document element, which is the value of the BPEL variable. The XPath variable binding will bind to the document element. For example, given the following schema definition:
<xsd:element name="StatusContainer">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="statusDescription" type="xs:string" form="qualified" />
</xsd:sequence>
</xsd:complexType>
</xsd:element>
And given the following variable declaration:
<variable name="AStatus" element="e:StatusContainer" />
Then a BPEL XPath expression to access the value of the statusDescription element, assuming the AStatus variable is in scope, would look like:
$Astatus/e:statusDescription
$AStatus points at the variable's document element, StatusContainer. So to access StatusMessage's child statusDescription it is only necessary to specify the child's element name.
BPEL variables declared using a complex type are manifested as a node-set XPath variable with one member node that contains the anonymous document element that itself contains the actual value of the BPEL complex type variable. The XPath variable binding will bind to the document element. For example, given the following schema definition:
<xs:complexType name="AuctionResults">
<xs:sequence>
<xs:element name="AuctionResult" maxOccurs="unbounded" form="qualified">
<xs:complexType>
<xs:attribute name="AuctionID" type="xs:int"/>
<xs:attribute name="Result" type="xs:string"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
And given the following variable declaration:
<variable name="AuctionResults" type="e:AuctionResults" />
Then a BPEL XPath expression to access the value of the second AuctionID attribute would look like:
$AuctionResults/e:AuctionResult[2]/@AuctionID
$AunctionResults points at the variable’s document element, AuctionResult[2] points to the second AuctionResult child of the document element, and @AuctionID points to the AuctionID attribute on the selected AuctionResult element.
WS-BPEL 2.0 messageType variables are manifested in XPath 1.0 as a series of variables, one variable per part in the messageType. Each variable is named by concatenating the message variable's name, the "." character and the local name of the part. The data in a BPEL messageType variable is NOT made available as one single XPath variable to general XPath processing under the default query and expression language binding. For example, if a messageType variable was named "myMessageTypeVar" and it contained two parts, "msgPart1" and "msgPart2" then XPath 1.0 binding that had "myMessageTypeVar" in scope would manifest two XPath 1.0 variables, $myMessageTypeVar.msgPart1 and $myMessageTypeVar.msgPart2. Please note that section 2.3 of [WSDL 1.1] requires that all part names within the same WSDL message definition must be unique.
WSDL message parts are always defined using either an XSD element, an XSD complex type or a XSD simple type. As such the manifestation of these message parts in XPath can be handled in the same manner as specified herein for element, complex type and simple type WS-BPEL 2.0 variables.
Below is a full example of how a WSDL message type is manifested in WS-BPEL 2.0 XPath.
<message name="StatusMessage">
<part name="StatusPart1" element="e:StatusContainer"/>
<part name="StatusPart2" element="e:StatusContainer"/>
</message>
And given the following variable declaration:
<variable name="StatusVariable" messageType="e:StatusMessage" />
Then a BPEL XPath expression to access the second part’s statusDescription element would look like:
$StatusVariable.StatusPart2/e:statusDescription
Note: It is possible to write XPath 1.0 queries that
can simultaneously query across multiple parts of a WSDL message variable by
applying a union operator to create one single nodeset. For example:
( $StatusVariable.StatusPart1 | $StatusVariable.StatusPart2 )//e:amount
BPEL simpleType variables are manifested directly as either an XPath string, Boolean or float object. If the XML schema type of the BPEL simpleType variable is xs:Boolean or any types that are restrictions of xs:Boolean then the BPEL variable will be manifested as an XPath Boolean object. If the XML schema type of the BPEL simpleType variable is xs:float, xs:int, xs:unsignedInt or any restrictions of those types then the BPEL variable will be manifested as an XPath float object. Any other XML schema types will be manifested as an XPath string object.
XPath 1.0 only has a single numeric object, float. Float is a 64 bit IEEE floating point number. However the resolution of the float object is not sufficient to capture the full value of some XML Schema data types. For example, a XSD decimal number must support at least 18 digits where as an XPath float only has to support approximately 16 digits. XSD numeric values that cannot be expressed without loss of accuracy as XPath float objects are instead translated into XPath string objects. XPath string objects can be explicitly translated into XPath float objects using the XPath number() function. Similarly if an XPath string object is used in a situation that calls for an XPath float object the XPath processor will automatically translate the XPath string object to an XPath float object. But implementers should be aware that if the accuracy of the XML schema type is greater than supported by the XPath float object then accuracy will be lost during the translation from string object to float object.
9.2.3 XPath 1.0 perspective and WS-BPEL
Section 1 of the XPath 1.0 specification [XPATH 1.0] defines five points that define the context in which an XPath expression is evaluated. Those points are reproduced below:
· a pair of non-zero positive integers (the context position and the context size)
· a set of variable bindings
· a function library
· the set of namespace declarations in scope for the expression
The following sections define how these contexts are initialized in BPEL for different types of BPEL expression and query language contexts.
9.2.4 Default use of XPath 1.0 for Expression and Query Languages
When XPath 1.0 is used for a Query or Expression Language, except as otherwise specified, the XPath context is initialized as follows:
· Context node = none
· Context position = none ; Context Size = none
· A set of variable bindings = variables visible to the Enclosing Element as defined by the BPEL scope rules
· A function library = core XPath and BPWS function libraries MUST be available and an engine specific function library MAY be available
· Namespace declaration = in-scope namespace declarations from Enclosing Element
It is worth emphasizing that as defined by the XPath 1.0 standard when resolving an XPath the namespace prefixes used inside of the variable (e.g. BPEL variables) are irrelevant. The only prefixes that matter are the in-scope namespaces.
For example, imagine a BPEL variable named “FooVar” of “foo” element type with value:
<a:foo xmlns:a="http://example.com"><a:bar >23</a:bar></a:foo>
The following XPath would return the value 23:
<from xmlns:b="http://example.com">$FooVar/b:bar/text()</from>
Notice that in the previous example the bar element is referred to use the 'b' namespace prefix rather than the 'a' namespace prefix that is used inside the actual value.
It is also worth emphasizing that XPath 1.0 explicitly requires that any element or attribute used in an XPath expression that does not have a namespace prefix must be treated as being namespace unqualified. That is, even if there is a default namespace defined on the enclosing element, the default namespace will not be applied.
Using the same value for Foo as provided previously the following would return a bpws:selectionFailure fault (in executable BPEL), because it fails to select any node:
<bpws:from xmlns="http://example.com">$FooVar/bar/text()</bpws:from>
The values inside of the XPath do not inherit the default namespace of the enclosing element. So the 'bar' element referenced in the XPath does not have any namespace value what so ever and therefore does not match with the bar element in the FooVar variable which has a namespace value of http://example.com.
Allowing BPEL variables to manifest as XPath variable bindings enables BPEL programmers to create powerful XPath expressions involving multiple BPEL variables. For example:
<assign>
<copy>
<from>$po/lineItem[@prodCode=$myProd]/amt * $exchangeRate</from>
<to>$convertedPO/lineItem[@prodCode=$myProd]/amt</to>
</copy>
</assign>
When XPath 1.0 is used as an expression or query language in BPEL, with the exception of propertyAlias definitions, there is no context node available. Therefore the legal values of the XPath Expr (http://www.w3.org/TR/xpath#NT-Expr) production must be restricted in order to prevent access to the context node.
Specifically, the "LocationPath" (http://www.w3.org/TR/xpath#NT-LocationPath) production rule of "PathExpr" (http://www.w3.org/TR/xpath#NT-PathExpr) production rule MUST NOT be used when XPath is used as an expression or query language (except in the case of propertyAlias which is covered separately). The previous restrictions on the XPath Expr production for the use of XPath as an expression language MUST be statically enforced.
The result of this restriction is that the "PathExpr" will always start with a "PrimaryExpr" (http://www.w3.org/TR/xpath#NT-PrimaryExpr) for BPEL expression or query language XPaths. It is worth remembering that PrimaryExprs are either variable references, expressions, literals, numbers or function calls, none of which can access the context node.
A query language is used when an lvalue needs to be returned. In addition to the previously listed restrictions, which except where otherwise indicated MUST apply to XPaths used as a query language, additional restrictions are also needed to ensure that the returned value of a query language expression is an lvalue. Specifically, when XPath is used as a query language the XPath MUST begin with a "VariableReference" and this restriction MUST be statically enforced.
9.2.5 Use of XPath 1.0 for Expression Languages in Join Conditions
When XPath 1.0 is used as an Expression Language for a join condition, the XPath context is initialized as follows:
· Context node = none
· Context position = none ; Context Size = none
· A set of variable bindings = links that the target the activity that the Enclosing Element is contained within
· A function library = the core XPath function library MUST be available, the BPWS function library MUST NOT be available and an engine specific function library MAY be available.
· Namespace declaration = in-scope namespace declarations from Enclosing Element
As explained in section 12.5.1 expressions in join conditions may only access the status of links that target the join condition's enclosing activity. No other data may be made available. To this end the only variable bindings made available to join conditions are ones that access link status. Also note that link status is only available in join conditions which is why links are not bound to XPath variables in any other context.
Link status is made available via XPath variable bindings by manifesting links that target the activity that contains the Enclosing Element as XPath variable bindings of identical name. That is, if there is a link called "ABC" that targets the activity then there must be an XPath variable binding called "ABC". Link variables are manifested as XPath Boolean objects whose value will be set to the Link's value.
Below is an example of a joinCondition inside of a <targets> element:
<targets>
<target
linkName="link1"/>
<target linkName="link2"/>
<joinCondition>$link1 and $link2</joinCondition>
</targets>
9.2.6 Use of XPath 1.0 for Query Languages in propertyAliases
When XPath 1.0 is used as Query Language for a propertyAlias, the XPath context is initialized as follows:
· Context node =
· When messageType/part attributes are used:
o If the message part is based on a complex type or an element, the context node will point to node-list containing a single node which is the EII for the referenced part where the EII is defined as specified in section 9.2.2.
o If the message part is based on a simple type, the context node will point to the XPath object specified for the particular variable type in section 9.2.2.
· When type attribute is used:
o If the type is a complex type, the context node will point to node-list containing a single node which is the EII for the referenced part where the EII is defined as specified in section 9.2.2.
o If the type is a simple type, the context node will point to the XPath object specified for the particular variable type in section 9.2.2.
· When element attribute is used, the context node will point to node-list containing a single node which is the EII for the referenced part where the EII is defined as specified in section 9.2.2.
· Context position = 1 ; Context Size = 1
· A set of variable bindings = There MUST NOT be any variable bindings available when XPath is used as query language in propertyAlias
· A function library = The core XPath function library MUST be available, the BPWS function library MUST NOT be available and an engine specific function library MAY be available.
· Namespace declaration = in-scope namespace declarations from Enclosing Element (note that in the past enclosing elements were always themselves enclosed within an activity, that is not the case here since propertyAliases are defined in WSDL files. But since there are no variable bindings to worry about this difference should not matter.)
propertyAlias is unique in BPEL in that it has a defined context node. Therefore none of the previously listed restrictions on the syntax of the XPath expression apply here. Any legal XPath expression may be used. It does not matter if an absolute or relative path is used in a propertyAlias as both will resolve to the context node since the context node in this case is the root node.
For example:
<propertyAlias propertyName="p:poId"
messageType="my:POMsg" part="poPart">
<query> po/id</query>
</propertyAlias>
Or
<propertyAlias propertyName="p:poId"
messageType="my:POMsg" part="poPart">
<query>(po/id + 1)</query>
</propertyAlias>
There is no requirement that property aliases return lvalues but it is worth pointing out that an attempt to assign to a property alias that doesn’t specify a lvalue will, as defined in section 9.3, fail with a bpws:selectionFailure.
9.44. Assignment
Copying data from one variable to another is a common task within a business process. The assign activity can be used to copy data from one variable to another, as well as to construct and insert new data using expressions. The use of expressions is primarily motivated by the need to perform simple computation (such as incrementing sequence numbers) that is required for describing business protocol behavior. Expressions operate on message selections, properties, and literal constants to produce a new value for a variable property or selection. This activity can also be used to copy endpoint references to and from partner links. Finally, it is possible to include extensible data manipulation operations defined as extension elements under namespaces different from the WS-BPEL namespace.
The assign assign contains one or more elementary assignments.
<assign validate="yes|no"? standard-attributes>
standard-elements
(<copy keepSrcElementName=”yes|no”> from-spec to-spec </copy> | <extensibleAssign> ...assign-element-of-other-namespace... </extensibleAssign>) +
</assign>
The assign activity allows copying a type-compatible value from the source ("from-spec") to the destination ("to-spec"), using the <copy> element. The from-spec MUST be one of the following forms except for the opaque form available in abstract processes:
<from variable="ncname" part="ncname"?/>
<from partnerLink="ncname" endpointReference="myRole|partnerRole"/>
<from variable="ncname" property="qname"/>
<from expressionLanguage="anyURI"?>expression</from>
<from> <literal> ... literal value ... </literal> </from>
The to-spec MUST be one of the following forms:
<to variable="ncname" part="ncname"?/>
<to partnerLink="ncname"/>
<to variable="ncname" property="qname"/>
<to queryLanguage="anyURI"?>… query … </to>To-specs MUST identify Lvalues so that assignment is possible. A Lvalue, in the context of XPATH 1.0, is a node-list containing a single node from the value store, e.g. variable, partnerLink, property, etc., identified by the to-spec that is to be replaced by the assignment. If a to-spec does not identify a Lvalue then a bpws:selectionFailure MUST be thrown.
In the first from-spec and to-spec variants the variable attribute provides the name of a variable. If the type of the variable is a WSDL messge type the optional part attribute MAY be used to provide the name of a part within that variable. When the variable is defined using XML Schema types (simple or complex)or element, the part attribute MUST NOT be used.
The second from-spec and to-spec variants allow dynamic manipulation of the endpoint references associated with partner links. The value of the partnerLink attribute is the name of a partnerLink declared in the process. In the case of from-specs, the role must also be specified because a process might need to communicate an endpoint reference corresponding to either its own role or the partner's role within the partnerLink. The value “myRole” means that the endpoint reference of the process with respect to that partnerLink is the source, while the value “partnerRole” means that the partner’s endpoint reference for the partnerLink is the source. For the to-spec, the assignment is only possible to the partnerRole, hence there is no need to specify the role. The type of the value used in partnerLink-style from/to-specs is always an endpoint reference (see Partner Link Types, Partner Links, and Endpoint References).
The third from-spec and to-spec variants allow explicit manipulation of varialbe properties (see Varialbe Properties) occurring in variables. The property value generated by the from-spec is generated in the same manner and with the same faults as the value returned by the getVariableProperty() function. The property forms are especially useful for abstract processes, because they provide a way to clearly define how distinguished data elements in messages are being used.
In the fourth (“expression”) from-spec variant, an expression language, identified by the optional expression language attribute, is used to return a value. In the fourth to-spec (“query”) variant, a query language, identified by the optional query language attribute, is used to return a value. Both from-spec and to-spec allow processes to perform simple computations on properties and variables (for example, increment a sequence number). This computed value MUST be one of the followings:
· a single XML information item other than a character information item (CharII): examples are element information item (EII) and attribute information item (AII)
·
a sequence of onezero or
more character information items: this is mapped to a Text Node or a String
in the XPath 1.0 data model of XPath
1.0
In the case of to-spec, the computed value MUST be a lvalue.
Please note that it is possible to use either the first form of from-spec/to-spec or the fourth form of from-spec/to-spec to perform copy on non-message-variables and parts of message variables, as this specification defines how to manifest non-message variables and parts of message variables as XML Infoset information items. However, only the first form of from-spec/to-spec is able to copy an entire message variable including all of its parts. Other from and to-spec forms are only able to refer to a single part in a WSDL message type variable and so cannot copy all of the parts at once.
If the execution of the query expression yields an unhandled query language fault, the WS-BPEL standard fault bpws:subLanguageExecutionFault MUST be thrown.
The fifth from-spec variant allows a literal value to be given as the source value to assign to a destination. The type of the literal value MUST be the type of the destination (to-spec). The type of the literal value MAY be optionally indicated inline with the value by using XML Schema's instance type mechanism (xsi:type).
The fifth from-spec variant allows a literal value to be given as the source value to assign to a destination. The type of the literal value MUST be the type as the destination (to-spec). The literal value to be assigned is included within a <literal> element in order prevent conflicts with standard extensibility elements under <from>; note that the <literal> element itself does not allow standard extensibility. The type of the literal value MAY be optionally indicated inline with the value by using XML Schema's instance type mechanism (xsi:type).
The fifth from-spec variant returns return values as if it were a from-spec that selects the children of the <literal> element in the WS-BPEL source code. Those return values MUST consist of Element Information Items or Text Information Items only. (See section “Selection Result of Copy Operations” for definition for Text Information Items) All XML parsing context of <literal> element in the source code, such as XML Namespace,are carried into the parsing children within <literal> element. An empty <literal /> element returns an empty Text Information Item. Here are some examples for illustration:
<assign>
<copy>
<from>
<literal xmlns:foo="http://foo.com">
<foo:bar />
</literal>
</from>
<to variable="myFooBarElemVar" />
</copy>
<copy>
<from>
<literal><!CDATA[[<foo:bar />]]></literal>
</from>
<to variable="myStringVar" />
</copy>
<copy>
<from> <literal/> </from>
<to variable="myStringVar"/>
</copy>
</assign>
The first <copy> above copies an <foo:bar /> element with “foo” prefix associated to “http://foo.com” namespace into “myFooBarElemVar”. The second <copy> copies a string which resembles “<foo:bar />” into “myStringVar”. The last <copy> copies an empty string into “myStringVar”.
The fifth from-spec variant also allows an endpoint reference literal value to be assign to a partnerLink directly, when used with the second variant of the to-spec. (see Partner Link Types, Partner Links, and Endpoint References).
In addition to <copy> specifications, other extensibility data manipulation elements MAY be included in an assign activity, inside an <extensibleAssign> element. The extensibility data manipulation elements MUST belong to a namespace different from the WS-BPEL namespace.
An optional keepSrcElementName attribute of the <copy> construct can be used to specify whether the element name of the destination (as selected by the to-spec) will be replaced by the element name of the source (as selected by the from-spec) during the copy operation. For details, please refer to Section 9.4.1, "Replacement Logic of Copy Operations.
An optional validate attribute can be used with the assign activity. When validate is set to "yes", it can be seen as a convenient marco of a combination of assign and validate activities. With validate="yes", the assign activity will validate all the variables being modified by the activity. E.g. variables being referenced in the to-specs.
The logic related to the validate attribute and assignment logic is considered as one unit of operation. If the "validate" parts of the operation fail, the whole assignment operation is considered as a failure also. When one of the variables is invalid against its correponding XML definition, a standard fault of "bpws:invalidVariables" fault MUST be thrown. Please note that the default of the validate attribute is "no".
A BPEL implementation MAY provide a mechanism to turn on/off any explicit validation. E.g. validate attribute at assign.
9.4.1 Selection Result of Copy Operations
There are 11 different types of information items
in the XML Infoset Information model. Most of these are not relevant in the
context of XML data manipulation as performed by <copy> operation
– examples include Processing Instruction Information Item, Comment
Information Item, and Document Type Declaration Information Item.
The selection result of the from-spec or to-spec used within a <copy> operation
MUST be one of the following three Information Items: Element Information Item
(EII), Attribute Information Item (AII), or Text Information Item (TII). Note
that EII and AII are defined in [Infoset], while TII is defined to bridge the
gap between the XML Infoset Model and other common XML data models, such as
XPath 1.0. TII is defined as follows:
Text Information Item (TII): This is an Information Item solely of which
an attribute points to a sequence of zero or more Character Information Items,
according to the document order; as such, a TII is not manifested in and of
itself directly in XML serialization When mapped to the XPath 1.0 model, it is
a generalization of String-Value (which has zero or more characters) and Text
Node (which has one or more characters). A TII LValue MUST NOT be empty. A TII
RValue MAY be mapped to a Text node, a String/Boolean/Number object in XPath
1.0, while a TII LValue MUST be mapped to a Text node.
If the selection result of a from-spec or a to-spec belongs to Information
Items other than EII, AII or TII, a bpws:selectionFailure fault MUST be thrown.
Note that if any of the unsupported Information Items are contained in the
selection result, they MUST be preserved; the only restriction is that they
MUST NOT be directly selected by the from-spec or the to-spec as the top-level
item.
In WS-BPEL, the <copy> operation
is essentially a one-to-one replacement operation. This requires that both the
from-spec and to-spec MUST select exactly one information item each, which
includes the case of one TII. Note that this restriction indicates that literal
values (the literal variant of from-spec) MUST only contain either a TII, or a
single EII, as its top-level value; when the RValue is an AII, a TII is
constructed from the normalized value property to be copied as specified in
Section 9.4.1, “Replacement Logic of Copy Operations”.
When using a partnerLink-based from-spec and to-spec, such as:
<from partnerLink="partnerLinkX" endpointReference="myRole|partnerRole" />
<to partnerLink="partnerLinkY" />
with another non-partnerLink-based from-spec and to-spec in a <copy> operation, these should be treated as if they produce an LValue and RValue of an EII of which [local name] is “service-ref” and [namespace name] is the WS-BPEL namespace[CB1] .
9.4.2 Replacement
Logic of Copy Operations
Replacement Logic for WSDL Message Variables
When the from-spec and to-spec of a <copy> operation both select
WSDL message variables, the following replacement logic MUST be executed:
The value
of the source message variable MUST be copied and the copy will become the
value of the destination message variable. The original value of the
destination message variable will no longer be available after the <copy>
operation.
Replacement Table for XML Data Item:
When the from-spec (Source) and to-spec (Destination) select one of three
Information Items types, a conforming WS-BPEL processor MUST use the
replacement rules for the combinations of Source and Destination Information
Item types for <copy> operation, as defined in the following Replacement
Logic Table:
|
Source\Destination |
EII |
AII |
TII |
|
EII |
RE |
RC |
RC |
|
AII |
RC |
RC |
RC |
|
TII |
RC |
RC |
RC |
Replacement Logic Table
Definitions
· RE (Replace-Element-properties):
o Replace the element at the destination with a copy of the entire element at the source, including [children] and [attribute] properties. An OPTIONAL keepSrcElementName attribute is provided to further refine the behavior:
§ The default value of the keepSrcElementName attribute is “no”, in which case the name (i.e. [namespace name] and [local name] properties) of the original destination element is used as the name of the resulting element.
§ When the keepSrcElementName attribute is set to “yes”, the source element name is used as the name of the resulting destination element
§ When the keepSrcElementName attribute is explicitly set, the selection results of the from-spec and to-spec MUST be elements. A BPEL processor MAY enforce this checking through static analysis of the expression/query language. If a violation is detected during runtime, a bpws:selectionFailure fault MUST be thrown.
· RC (Replace-Content):
o To obtain the source content:
§ The source (from-spec) MUST yield one and only one Information Item. Otherwise, a selectionFailure fault MUST be thrown.
§ Once the Information Item is yielded from the source, a TII will be computed based on the source Information Item as the source content. The source content TII is based on a series of Character Information Items, generally based on the document order (unless a sorting specification is present in the underlying expression or query), taken from the returned Information Item. These Character Information Items are copied, concatenated, and the resulting value assigned to the TII. This is semantically similar to the use of the XPath 1.0 "string()" function.
§ If the source is an EII with an xsi:nil="true", a selectionFailure fault MUST be thrown (where this check is performed during EII-to-AII or EII-to-TII copy).,
o To replace the content:
§ If the destination is an EII, remove all [children] properties (if any) and add the source content TII as the child of the EII.
§ If the destination is an AII, replace the value of AII with the TII from the source. The value MUST be normalized, in accordance with the XML 1.0 Recommendation (section 3.3.3 Attribute Value Normalization: http://www.w3.org/TR/1998/REC-xml-19980210#AVNormalize).
§ If the destination is a TII, replace the TII in the destination with the TII from the source.
Note that:
· Attribute values are not text nodes in XPath 1.0. Attribute nodes have a string value that corresponds to the XML normalized attribute value, which is a TII.
· Information Items referenced by the to-spec MUST be an LValue. In the XPath 1.0 data model, a TII LValue MUST be a Text Node.
· When the to-spec selects a TII (e.g. Text node in XPath 1.0) as LValue, and the TII does NOT belong to a WS-BPEL variable of an XSD string type or a type derived from XSD string , and one of the followings is computed or selected as RValue from the from-spec:
o a TII which has zero Character Information Item
o an AII which has an empty string as its [normalized value]
o an EII which has zero Character Information Item as its descendants, that is its [children] and nested [children]. (Note: applying XPath 1.0 String() function to this kind of EII would yield an empty string)
then a bpws:mismatchedAssignmentFailure fault MUST be thrown
Using <copy> to initialize variables
When the destination (either an entire BPEL variable or message part) selected by the to-spec in <copy> is un-initialized, the destination variable or message part MUST first be initialized before executing the above replacement logic. The initialization details are as follows:
· For complex type and simple type variables, a skeleton structure, composed of a DII and an anonymous EII (Document Element), will be created as an integral part of the initialization of the <assign>/<copy> operation. Once this skeleton structure is created, the above "replacement" logic can be reused.
· For element based variables, a skeleton structure, composed of a DII and an EII (Document Element) with the name matching the element name used in variable declaration, will be created as an integral part of the initialization of the <assign>/<copy> operation. Once this skeleton structure is created, the above "replacement" logic can be reused.
· For an uninitialized message part, the above two blocks of logic are reused, as a message part is either of simple type, complex type, or an element.
Handling Non- XML-Infoset Data Objects in <copy>
Simple type variables and values MAY be allowed to manifest as non-XML-Infoset data objects, such as boolean, string, or float, as defined in XPath 1.0. Some expressions may yield such a non-XML-Infoset data object, for example:
<from> number($order/amt) * 0.8 </from>
To consistently apply the above replacement logic, such non-XML-Infoset data are handled as Text Information Items (TII). This logic is achieved through "to-string" data conversion, as TII resembles a string object. More specifically, when the XPath 1.0 data model is used in WS-BPEL, "string(object)" (http://www.w3.org/TR/1999/REC-xpath-19991116#function-string) coercion MUST be used to convert boolean or number objects to String/TII.
Note that this conversion is used to describe the expected result of <copy>. A WS-BPEL processor MAY skip the actual conversion for optimization if the result of <copy> remains the same, which would render the conversion redundant.
XML Namespace Preservation
In the <copy> operation, the [in-scope namespaces] properties (similar to other XML Infoset Item properties) from the source MUST be preserved in the result at the destination. For example, when variables are serialized into XML text, a WS-BPEL processor will make use of a namespace-aware XML infrastructure, which maintains the XML Namespace consistency in the XML text, where in such a case the infrastructure adds XML Namespace declarations or renames prefixes used in XML Namespaces; where these properties can be placed in the Infoset is at the discretion of the implementor of the XML infrastructure
A precautionary note: In some XML Schema designs, QName may be used for attribute or element values. For example, where the value of attrX is a QName ("myPrefix:somename") and the value of "foo:bar3" is another QName ("myPrefix:somename2")
<foo:bar1 xmlns:myPrefix="http://my.com"
xmlns:foo="http://foo.com">
<foo:bar2 attrX="myPrefix:somename" />
<foo:bar3>myPrefix:somename2</foo:bar3>
</foo:bar1>
When the correponding TII and AII are selected via a schema-unaware expression/query language, its schema-unaware data model will fail to capture the namespace properties of any such QName-based attribute and element values. Therefore, there is the potential for the XML namespace to be lost. WS-BPEL developers should be aware that, XPath 1.0, the default expression and query language of WS-BPEL, is schema unaware.
Using the same sample data
from above for illustration, when "foo:bar2/@attrX" is copied
as the source with XPath 1.0 data model, the namespace declaration for "myPrefix" might be
missing in the destination.
Examples illustrating the replacement logic of copy operations: (this is pending editor group’s decision on incorporating examples in the specification text)
(a) Copying EII-to-EII
XML Schema Context
<xs:element name="poHeader">
<xs:complexType>
<xs:sequence>
<xs:choice>
<xs:element name="shippingAddr" type="tns:AddressType"/>
<xs:element name="USshippingAddr" type="tns:USAddressType"/>
</xs:choice>
<xs:element name="billingAddr" type="tns:AddressType"/>
</xs:sequence>
</xs:complexType>
</xs:element>
"tns:USAddressType" is a type
extended from "tns:AddressType".
·
Example 1
<assign>
<copy>
<from>$poHeaderVar1/tns:shippingAddr</from>
<to>$poHeaderVar2/tns:billingAddr</to>
</copy>
</assign>
The above <copy> will replace the attributes and elements of the billing address in "poHeaderVar2" with those of shipping address in "poHeaderVar1".
Value of poHeaderVar1
<tns:poHeader>
...
<tns:shippingAddr verified="true">
<tns:street>123 Main Street</tns:street>
<tns:city>SomeWhere City</tns:city>
<tns:country>UK</tns:state>
</tns:shippingAddr>
...
</tns:poHeader>
Value of poHeaderVar2: (before the copy)
<tns:poHeader>
...
<tns:billingAddr pobox="true" />
...
</tns:poHeader>
Value of poHeaderVar2: (after the copy)
<tns:poHeader>
...
<tns:billingAddr verified="true">
<tns:street>123 Main Street</tns:street>
<tns:city>SomeWhere City</tns:city>
<tns:country>UK</tns:state>
</tns:billingAddr>
...
</tns:poHeader>
·
Example 2
<assign>
<copy keepSrcElementName="yes">
<from>$poHeaderVar3/tns:USshippingAddr</from>
<to>$poHeaderVar2/tns:shippingAddr</to>
</copy>
</assign>
Value of poHeaderVar3
<tns:poHeader>
...
<tns:USshippingAddr verified="true">
<tns:street>123 Main Street</tns:street>
<tns:city>SomeWhere City</tns:city>
<tns:country>USA</tns:state>
<tns:zipcode>98765</tns:zipcode>
</tns:USshippingAddr>
...
</tns:poHeader>
Value of poHeaderVar2: (before the copy)
<tns:poHeader>
...
<tns:shippingAddr pobox="true" />
...
</tns:poHeader>
Value of poHeaderVar2: (after the copy)
<tns:poHeader>
...
<tns:USshippingAddr verified="true">
<tns:street>123 Main Street</tns:street>
<tns:city>SomeWhere City</tns:city>
<tns:country>USA</tns:state>
<tns:zipcode>98765</tns:zipcode>
</tns:USshippingAddr>
...
</tns:poHeader>
(b) EII-to-AII
XML Data Context
Value of creditApprovalVar:
<tns:creditApplication appId="123-456">
<tns:approvedLimit code="AXR">4500</tns:approvedLimit>
</tns:creditApplication>
· Example 1
<assign>
<copy>
<from>$creditApprovalVar/tns:approvedLimit</from>
<to>$approvalNotice2Var/@amt</to>
</copy>
</assign>
Value of approvalNotice2Var: (before the copy)
<tns2:approvalNotice amt=”” />
Value of approvalNotice2Var: (after the copy)
<tns2:approvalNotice amt="4500" />
( c ) EII-to-TII
XML Data Context
Value of creditApprovalVar:
<tns:creditApplication appId="123-456">
<tns:approvedLimit code="AXR">4500</tns:approvedLimit>
</tns:creditApplication>
· Example 1
<assign>
<copy>
<from>$creditApprovalVar/tns:approvedLimit</from>
<to>$approvalNotice3Var/text()</to>
</copy>
</assign>
Value of approvalNotice3Var: (before <copy>)
<tns3:approvalNotice>0</tns3:approvalNotice>
Value of approvalNotice3Var: (after <copy>)
<tns3:approvalNotice>4500</tns3:approvalNotice>
·
Example 2
<assign>
<copy>
<from>$creditApprovalVar/tns:approvedLimit</from>
<to>$approvalNotice4Var/text()</to>
</copy>
</assign>
Value of approvalNotice4Var: (before <copy>)
<tns4:approvalNotice></tns4:approvalNotice>
Since there is no text node under"tns4:approvalNotice", selectionFailure fault will be thrown. No replacment logic will be executed.
· Example 3: EII-to-EII for direct comparison to EII-to-TII
<assign>
<copy>
<from>$creditApprovalVar/tns:approvedLimit</from>
<to>$approvalNotice4Var</to>
</copy>
</assign>
Value of approvalNotice4Var: (before <copy>)
<tns4:approvalNotice></tns4:approvalNotice>
Value of approvalNotice4Var: (after an EII-to-EII <copy>)
<tns4:approvalNotice code="AXR">4500</tns4:approvalNotice>
(d) AII-to-AII
XML Data Context
Value of orderDetailVar:
<tns:orderDetail amt="2299"/>
· Example 1
<assign>
<copy>
<from>$orderDetailVar/@amt</from>
<to>$billingDetailVar/@amt</to>
</copy>
</assign>
Value of billingDetailVar: (before <copy>)
<tns:billingDetail amt="" />
Value of billingDetailVar: (after <copy>)
<tns:billingDetail amt="2299" />
(e) AII-to-EII
XML Data Context
Value of orderDetailVar:
<tns:orderDetail amt="3399" />
· Example 1
<assign>
<copy>
<from>$orderDetailVar/@amt</from>
<to>$billingDetailVar/tns1:billingAmount</to>
</copy>
</assign>
Value of billingDetailVar: (before <copy>)
<tns1:billingDetail id="8675309">
<tns1:billingAmount code="F00B2R"></tns1:billingAmount>
</tns1:billingDetail>
Value of billingDetailVar: (after <copy>)
<tns1:billingDetail id="8675309">
<tns1:billingAmount code="F00B2R">3399</tns1:billingAmount>
</tns1:billingDetail>
(f) AII-to-TII
XML Data context.
Value of orderDetailVar:
<tns:orderDetail amt="4499" />
· Example 1
<assign>
<copy>
<from>$orderDetailVar/@amt</from>
<to>$billingAmount2Var/text()</to>
</copy>
</assign>
Value of billingAmount2Var: (before <copy>)
<tns2:billingAmount>0</tns2:billingAmount>
Value of billingAmount2Var: (after <copy>)
<tns2:billingAmount>4499</tns2:billingAmount>
(g) TII-to-TII
XML Data context
Value of postalCodeVar:
<tns:postalCode>95110</tns:postalCode>
· Example 1
<assign>
<copy>
<from>$postalCodeVar/text()</from>
<to>$shippingPostalCodeVar/text()</to>
</copy>
</assign>
Value of shippingPostalCodeVar: (before <copy>)
<tns:shippingPostalCode>0</tns:shippingPostalCode>
Value of shippingPostalCodeVar: (after <copy>)
<tns:shippingPostalCode>95110</tns:shippingPostalCode>
(h) TII-to-AII
XML Data Context
Value of postalCodeVar:
<tns:postalCode>94304</tns:postalCode>
· Example 1
<assign>
<copy>
<from>$postalCodeVar/text()</from>
<to>$shippingAddress1Var/@postCode</to>
</copy>
</assign>
Value of shippingAddress1Var: (before <copy>)
<tns1:shippingAddress postCode="" />
Value of approvalNotice1Var: (after <copy>)
<tns1:shippingAddress postCode="94304" />
(i) TII-to-EII
XML Data Context
Value of postalCodeVar:
<tns:postalCode>94107</tns:postalCode>
· Example 1
<assign>
<copy>
<from>$postalCodeVar/text()</from>
<to>$shippingAddress2Var/tns2:postalCode</to>
</copy>
</assign>
Value of shippingAddress2Var: (before <copy>)
<tns2:shippingAddress id="9035768">
<tns2:postalCode></tns2:postalCode>
</tns2:shippingAddress>
Value of shippingAddress2Var: (after <copy>)
<tns2:shippingAddress id="9035768">
<tns2:postalCode>94107</tns:postalCode>
</tns2:shippingAddress>
9.4.31. Type
Compatibility in Copy OperationsAssignment
For an assignmenta copy operation
to be valid, the data referred to by the from and the to
specifications MUST be of compatible types. The following points make this
precise:
· The selection result of the from-spec is a variable of a WSDL message type and the selection result of the to-spec is a variable of a WSDL message type. In this case both variables MUST be of the same message type, where two message types are said to be equal if their qualified names are the same.
· The selection result of the from-spec is a variable of a WSDL message type and the selection result of the to-spec is not, or vice versa. This is not legal because parts of variables, selections of variable parts, or endpoint references cannot be assigned to/from variables of WSDL message types directly.
·
In all other cases,
the types of the source and destination are XML Schema types or elements, and
the constraint is that the source value MUST possess the element or type
associated with the destination. Note that this does not require the types
associated with the source and destination to be the same. In particular, the
source type MAY be a subtype of the destination type. In the case of variables
defined by reference to an element, moreover, both the source and the target
MUST be the same element.
The semantics of a process in which any of the
matching constraints above is violated is undefined.
9.4.2. Assignment Example
The example assumes the following complex type definition in the namespace "http://tempuri.org/bpws/example":
<complexType name="tAddress">
<sequence>
<element name="number" type="xsd:int"/>
<element name="street" type="xsd:string"/>
<element name="city" type="xsd:string"/>
<element name="phone">
<complexType>
<sequence>
<element name="areacode" type="xsd:int"/>
<element name="exchange" type="xsd:int"/>
<element name="number" type="xsd:int"/>
</sequence>
</complexType>
</element>
</sequence>
</complexType>
<element name = “address” type = “tAddress”/>
Assume that the following WSDL message definition exists for the same target namespace:
<message name="person" xmlns:x="http://tempuri.org/bpws/example">
<part name="full-name" type="xsd:string"/>
<part name="address" element="x:address"/>
</message>
Also assume the following WS-BPEL variable declarations:
<variable name="c1" messageType="x:person"/>
<variable name="c2" messageType="x:person"/>
<variable name="c3" element="x:address"/>
The example illustrates copying one variable to another as well as copying a variable part to a variable of compatible element type:
<assign>
<copy>
<from variable="c1"/>
<to variable="c2"/>
</copy>
<copy>
<from>$c1.address</from>
<to variable="c3"/>
</copy>
</assign>
10. Correlation
The information provided so far suggests that the target for messages that are delivered to a business process service is the WSDL port of the recipient service. This is an illusion because, by their very nature, stateful business processes are instantiated to act in accordance with the history of an extended interaction. Therefore, messages sent to such processes need to be delivered not only to the correct destination port, but also to the correct instance of the business process that provides the port. The infrastructure hosting the process must do this in a generic manner, to avoid burdening every process implementation with the need to implement a custom mechanism for instance routing. Messages, which create a new business process instance, are a special case, as described in The Lifecycle of a Business Process.
In the object-oriented world, such stateful interactions are mediated by object references, which intrinsically provide the ability to reach a specific object (instance) with the right state and history for the interaction. This works reasonably well in tightly coupled implementations where a dependency on the structure of the implementation is normal. In the loosely coupled world of Web Services, the use of such references would create a fragile web of implementation dependencies that would not survive the independent evolution of business process implementation details at each business partner. In this world, the answer is to rely on the business data and communication protocol headers that define the wirelevel contract between partners and to avoid the use of implementation-specific tokens for instance routing whenever possible.
Consider the usual supply-chain situation where a buyer sends a purchase order to a seller. Suppose that the buyer and seller have a stable business relationship and are statically configured to send documents related to the purchasing interaction to the URLs associated with the relevant WSDL service ports. The seller needs to asynchronously return an acknowledgement for the order, and the acknowledgement must be routed to the correct business process instance at the buyer. The obvious and standard mechanism to do this is to carry a business token in the order message (such as a purchase order number) that is copied into the acknowledgement for correlation. The token can be in the message envelope in a header or in the business document (purchase order) itself. In either case, the exact location and type of the token in the relevant messages is fixed and instance independent. Only the value of the token is instance dependent. Therefore, the structure and position of the correlation tokens in each message can be expressed declaratively in the business process description. The WS-BPEL notion of correlation set, described in the following section, provides this feature. The declarative information allows a WS-BPEL-compliant infrastructure to use correlation tokens to provide instance routing automatically.
The declarative specification of correlation relies on declarative properties of messages. A property is simply a "field" within a message identified by a query—by default the query language is XPath 1.0. This is only possible when the type of the message part or binding element is described by using an XML Schema. The use of correlation tokens and endpoint references is restricted to message parts described in this way. To be clear, the actual wire format of such types can still be non-XML, for example, EDI flat files, based on different bindings for port types.
10.1. Message Correlation
During its lifetime, a business process instance typically holds one or more conversations with partners involved in its work. Conversations may be based on sophisticated transport infrastructure that correlates the messages involved in a conversation by using some form of conversation identity and routes them automatically to the correct service instance without the need for any annotation within the business process. However, in many cases correlated conversations involve more than two parties or use lightweight transport infrastructure with correlation tokens embedded directly in the application data being exchanged. In such cases, it is often necessary to provide additional application-level mechanisms to match messages and conversations with the business process instances for which they are intended.
Correlation patterns can become quite complex. The use of a particular set of correlation tokens does not, in general, span the entire interaction between a service instance and a partner (instance), but spans a part of the interaction. Correlated exchanges may nest and overlap, and messages may carry several sets of correlation tokens. For example, a buyer might start a correlated exchange with a seller by sending a purchase order (PO) and using a PO number embedded in the PO document as the correlation token. The PO number is used in the PO acknowledgement by the seller. The seller might later send an invoice that carries the PO number, to correlate it with the PO, and also carries an invoice number so that future payment-related messages need to carry only the invoice number as the correlation token. The invoice message thus carries two separate correlation tokens and participates in two overlapping correlated exchanges.
WS-BPEL addresses correlation scenarios by providing a declarative mechanism to specify correlated groups of operations within a service instance. A set of correlation tokens is defined as a set of properties shared by all messages in the correlated group. Such a set of properties is called a correlation set.
Correlation sets are declared within scopes and associated with them in a manner that is analogous to variable declarations. Each correlation set is declared within a scope and is said to belong to that scope. Correlation sets that belong to the global process scope are called global correlation sets. Correlation sets may also belong to other, non-global scopes, and such correlation sets are called local correlation sets. Each correlation set is only visible in the scope in which it is defined and in all scopes nested within the scope it belongs to. Thus, global correlation sets are visible throughout the process. The name of a correlation set MUST be unique amongst the names of all correlation sets defined within the same immediately enclosing scope. This requirement MUST be statically enforced. It is possible to "hide" a correlation set in an outer scope by declaring a correlation set with an identical name in an inner scope.
A global correlation set is in an uninitiated state at the beginning of a process. A local correlation set is in an uninitiated state at the start of the scope it belongs to. Note that non-global scopes in general start and complete their behavior more than once in the lifetime of the process instance they belong to.
Correlation sets resemble late-bound constants rather than variables in their semantics. The binding of a correlation set is triggered by a specially marked message send or receive operation. A correlation set can be initiated only once during the lifetime of the scope it belongs to. Thus, a global correlation set can only be initiated at most once during the lifetime of the process instance. Its value, once initiated, can be thought of as an alias for the identity of the business process instance. A local correlation set is available for binding each time the corresponding scope starts, but once initiated must retain its value until the scope completes.
In multiparty business protocols, each participant process in a correlated message exchange acts either as the initiator or as a follower of the exchange. The initiator process sends the first message (as part of an operation invocation) that starts the conversation, and therefore defines the values of the properties in the correlation set that tag the conversation. All other participants are followers that bind their correlation sets in the conversation by receiving an incoming message that provides the values of the properties in the correlation set. Both initiator and followers must mark the first activity in their respective groups as the activity that binds the correlation set.
10.2. Defining and Using Correlation Sets
The examples in this section show correlation being used on almost every messaging activity (receive, reply, and invoke). This is because WS-BPEL does not assume the use of any sophisticated conversational transport protocols for messaging. In cases where such protocols are used, the explicit use of correlation in WS-BPEL can be reduced to those activities that establish the conversational connections.
Each correlation set in WS-BPEL is a named group of properties that, taken together, serve to define a way of identifying an application-level conversation within a business protocol instance. A given message can carry multiple correlation sets. After a correlation set is initiated, the values of the properties for a correlation set must be identical for all the messages in all the operations that carry the correlation set and occur within the corresponding scope until its completion. This correlation consistency constraint MUST be observed in all cases of initiate values. The legal values of the initiate attribute are: "yes", "join", "no". The default value of the initiate attribute is "no".
· When the initiate attribute is set to "yes", the related activity MUST attempt to initiate the correlation set.
o If the correlation set is already initiated and the initiate attribute is set to "yes", the semantics is undefined.
· When the initiate attribute is set to "join", the related activity MUST attempt to initiate the correlation set, if the correlation set is NOT initiated yet.
o If the correlation set is already initiated and the initiate attribute is set to "join", the correlation consistency constraint MUST be observed. If the constraint is violated, the semantics is undefined.
· When the initiate attribute is set to "no", the related activity MUST NOT attempt to initiate the correlation set.
o If an activity with the "initiate" attribute set to "no" attempts to use a correlation set that has not been previously initiated, the semantics is undefined.
o If the correlation set is already initiated and the initiate attribute is set to "no", the correlation consistency constraint MUST to be observed. If the constraint is violated, the semantics is undefined.
If multiple correlation sets are used in a message activity, then the consistency constraint MUST be observed for all correlation sets used. For example, the correlation sets used in an inbound message activity (e.g. receive) must all match message for that message to be delivered to the activity in the given process instance. If one of initiated correlation set does NOT match with the message, the semantics is undefined.
As the following examples illustrate, a correlation set is initiated when the activity within which it is used applies the attribute initiate="yes" to the set.
<correlationSets>?
<correlationSet name="ncname" properties="qname-list"/>+
</correlationSets>
Following is an extended example of correlation. It begins by defining four message properties: customerID, orderNumber, vendorID and invoiceNumber. All of these properties are defined as part of the "http://example.com/supplyCorrelation.wsdl" namespace defined by the document.
<definitions name="properties"
targetNamespace="http://example.com/supplyCorrelation.wsdl"
xmlns:tns="http://example.com/supplyCorrelation.wsdl"
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!-- define correlation properties -->
<bpws:property name="customerID" type="xsd:string"/>
<bpws:property name="orderNumber" type="xsd:int"/>
<bpws:property name="vendorID" type="xsd:string"/>
<bpws:property name="invoiceNumber" type="xsd:int"/>
</definitions>
Note that these properties are global names with known (simple) XMLSchema types. They are abstract in the sense that their occurrence in variables needs to be separately specified (see Variable Properties). The example continues by defining purchase order and invoice messages and by using the concept of aliasing to map the abstract properties to fields within the message data identified by selection.
<definitions name="correlatedMessages"
targetNamespace="http://example.com/supplyMessages.wsdl"
xmlns:tns="http://example.com/supplyMessages.wsdl"
xmlns:cor=http://example.com/supplyCorrelation.wsdl xmlns:po = “http://example.com/po.xsd”
xmlns="http://schemas.xmlsoap.org/wsdl/">
<!—define schema types for PO and invoice information -->
<types>
<xsd:schema targetNamespace = “http://example.com/po.xsd”>
<xsd:complexType name="PurchaseOrder">
<xsd:element name="CID" type="xsd:string"/>
<xsd:element name="order" type="xsd:int"/>
...
</xsd:complexType>
<xsd:complexType name="PurchaseOrderResponse">
<xsd:element name="CID" type="xsd:string"/>
<xsd:element name="order" type="xsd:int"/>
<xsd:element name="VID" type="xsd:string"/>
<xsd:element name="invNum" type="xsd:int"/>
...
</xsd:complexType>
<xsd:complexType name="PurchaseOrderRejectType">
<xsd:element name="CID" type="xsd:string"/>
<xsd:element name="order" type="xsd:int"/>
<xsd:element name="reason" type="xsd:string"/>
...
</xsd:complexType>
<xsd:complexType name="InvoiceType">
<xsd:element name="VID" type="xsd:string"/>
<xsd:element name="invNum" type="xsd:int"/>
</xsd:complexType> <xsd:element name = “PurchaseOrderReject” type= “po:PurchaseOrderRejectType”> <xsd:element name = “Invoice” type= “po:invoiceType”>
</xsd:schema>
</types>
<message name="POMessage">
<part name="PO" type="po:PurchaseOrder"/>
</message>
<message name="POResponse">
<part name="RSP" type="po:PurchaseOrderResponse"/>
</message>
<message name="POReject">
<part name="RJCT" element="po:PurchaseOrderReject"/>
</message>
<message name="InvMessage">
<part name="IVC" element = “po:Invoice"/>
</message>
<bpws:propertyAlias propertyName="cor:customerID"
messageType="tns:POMessage" part="PO">
<bpws:query> CID </bpws:query></bpws:propertyAlias>
<bpws:propertyAlias propertyName="cor:orderNumber"
messageType="tns:POMessage" part="PO">
<query> Order </query></bpws:propertyAlias>
<bpws:propertyAlias propertyName="cor:customerID"
messageType="tns:POResponse" part="RSP">
<bpws:query> CID </bpws:query></bpws:propertyAlias>
<bpws:propertyAlias propertyName="cor:orderNumber"
messageType="tns:POResponse" part="RSP">
<query> Order </query></bpws:propertyAlias>
<bpws:propertyAlias propertyName="cor:vendorID"
messageType="tns:POResponse" part="RSP">
<query> VID </query></bpws:propertyAlias>
<bpws:propertyAlias propertyName="cor:invoiceNumber"
messageType="tns:POResponse" part="RSP">
<query> InvNum </query></bpws:propertyAlias>
<bpws:propertyAlias propertyName="cor:vendorID"
messageType="tns:InvMessage" part="IVC">
<query> VID </query></bpws:propertyAlias>
<bpws:propertyAlias propertyName="cor:invoiceNumber"
messageType="tns:InvMessage" part="IVC">
<query> InvNum </query></bpws:propertyAlias>
...
</definitions>
Finally, the portType used is defined, in a separate WSDL document.
<definitions name="purchasingPortType"
targetNamespace="http://example.com/puchasing.wsdl"
xmlns:smsg="http://example.com/supplyMessages.wsdl"
xmlns="http://schemas.xmlsoap.org/wsdl/"> <! – import supplyMessage.wsdl -- >
<portType name="PurchasingPT">
<operation name="SyncPurchase">
<input message="smsg:POMessage"/>
<output message="smsg:POResponse"/>
<fault name="tns:RejectPO" message="smsg:POReject"/>
</operation>
<operation name="AsyncPurchase">
<input message="smsg:POMessage"/>
</operation>
</portType>
<portType name="BuyerPT">
<operation name="AsyncPurchaseResponse">
<input message="smsg:POResponse"/>
</operation>
<operation name="AsyncPurchaseReject">
<input message="smsg:POReject"/>
</operation>
</portType>
</definitions>Both the properties and their mapping to purchase order and invoice messages will be used in the following correlation examples.
<correlationSets
xmlns:cor="http://example.com/supplyCorrelation.wsdl">
<!-- Order numbers are particular to a customer,
this set is carried in application data -->
<correlationSet name="PurchaseOrder"
properties="cor:customerID cor:orderNumber"/>
<!-- Invoice numbers are particular to a vendor,
this set is carried in application data -->
<correlationSet name="Invoice"
properties="cor:vendorID cor:invoiceNumber"/>
</correlationSets>
Correlation set names are used in invoke, receive, and reply activities (see Invoking Web Service Operations and Providing Web Service Operations), in the onMessage branches of pick activities, and in the onEvent variant of event handlers (see Pick and Message Events). These sets are used to indicate which correlation sets (i.e., the corresponding property sets) occur in the messages being sent and received. The initiate attribute is used to indicate whether the set is being initiated. When the attribute is set to "yes" the set is initiated with the values of the properties occurring in the message being sent or received. (Please see the beginning of this section for details of of initiate attribute.) Finally, in the case of invoke, when the operation invoked is synchronous request/response, a pattern attribute is used to indicate whether the correlation applies to the outbound (request) message, the inbound (response) message, or both. These ideas are explained in more detail in the context of the use of correlation in the rest of this example.
A message can carry the tokens of one or more correlation sets. The first example shows an interaction in which a purchase order is received in a one-way inbound request and a confirmation including an invoice is sent in the asynchronous response. The PurchaseOrder correlationSet is used in both activities so that the asynchronous response can be correlated to the request at the buyer. The receive activity initiates the PurchaseOrder correlationSet. The buyer is therefore the initiator and the receiving business process is a follower for this correlationSet. The invoke activity sending the asynchronous response also initiates a new correlationSet Invoice. The business process is the initiator of this correlated exchange and the buyer is a follower. The response message is thus a part of two separate conversations, and forms the bridge between them.
In the following, the prefix SP: represents the namespace "http://example.com/puchasing.wsdl".
<receive partnerLink="Buyer" portType="SP:PurchasingPT"
operation="AsyncPurchase"
variable="PO">
<correlations>
<correlation set="PurchaseOrder" initiate="yes"/>
</correlations>
</receive>
<invoke partnerLink="Buyer" portType="SP:BuyerPT"
operation="AsyncPurchaseResponse" inputVariable="POResponse">
<correlations>
<correlation set="PurchaseOrder" initiate="no" pattern="out"/>
<correlation set="Invoice" initiate="yes" pattern="out"/>
</correlations>
</invoke>
Alternatively, the response might have been a rejection (such as an "out-of-stock" message), which in this case terminates the conversation correlated by the correlationSet PurchaseOrder without starting a new one correlated with Invoice. Note that the initiate attribute is missing. It therefore has the default value of "no".
<invoke partnerLink="Buyer" portType="SP:BuyerPT"
operation="AsyncPurchaseReject" inputVariable="POReject">
<correlations>
<correlation set="PurchaseOrder" pattern="out"/>
</correlations>
</invoke>
The use of correlation with synchronous Web Service invocation is illustrated by the alternative synchronous purchasing operation used by an invoke activity used in the buyer's business process.
<invoke partnerLink="Seller" portType="SP:PurchasingPT"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
<correlations>
<correlation set="PurchaseOrder" initiate="yes" pattern="out"/>
<correlation set="Invoice" initiate="yes" pattern="in"/>
</correlations>
<catch faultName="SP:RejectPO" faultVariable="POReject" faultMessageType="smsg:POReject">
<!-- handle the fault -->
</catch>
</invoke>
Note that an invoke consists of two messages: an outgoing request message and an incoming reply message. The correlation sets applicable to each message must be separately considered because they can be different. In this case the PurchaseOrder correlation applies to the outgoing request that initiates it, while the Invoice correlation applies to the incoming reply and is initiated by the reply. Because the PurchaseOrder correlation is initiated by an outgoing message, the buyer is the initiator of that correlation but a follower of the Invoice correlation because the values of the correlation properties for Invoice are initiated by the seller in the reply received by the buyer.
11. Basic Activities
11.1. Standard Attributes for Each Activity
Each activity has optional standard attributes: a name and an indicator whether a join fault should be suppressed if it occurs. See Flow for a full discussion of the suppressJoinFailure attribute. The name attribute is used to provide machine processable names for activities although currently the BPEL specification only makes programmatic use of the names of scope activities. The name of a named activity MUST be unique amongst all named activities present within the same immediately enclosing scope. This requirement MUST be statically enforced.
name="ncname"?
suppressJoinFailure="yes|no"?>
When the suppressJoinFailure attribute is not specified for an activity, it inherits its value from its closest enclosing activity or from the process if no enclosing activity specifies this attribute.
11.2. Standard Elements for Each Activity
Each WS-BPEL activity has nested standard elements <source> and <target> within the optional containers <sources> and <targets>. The use of these elements is required for establishing synchronization relationships through links (see Flow). Each link is defined independently and given a name. The link name is used as value of the linkName attribute of the <source> element. An activity MAY declare itself to be the source of one or more links by including one or more <source> elements. Each <source> element MUST use a distinct link name. Similarly, an activity MAY declare itself to be the target of one or more links by including one or more <target> elements. Each <source> element associated with a given activity MUST use a link name distinct from all other <source> elements at that activity. Each <target> element associated with a given activity MUST use a link name distinct from all other <target> elements at that activity. Each <source> element MAY optionally specify a transition condition that functions as a guard for following this specified link (see Flow). If the transition condition is omitted, it is deemed to be present with the constant value true.
<sources>? <source linkName="ncname">+<transitionCondition expressionLanguage="anyURI"?>?
... bool-expr ... </transitionCondition>
</source></sources>
<targets>?
<joinCondition expressionLanguage="anyURI"?>?... bool-expr ...
</joinCondition> <target linkName="ncname"/>+</targets>?
The value of the <joinCondition> element is a Boolean-valued expression in the expression language indicated by the expressionLanguage attribute, or in the default expression language for this process (see Expressions). If no join condition is specified, the join condition is the logical OR of the link status of all incoming links of this activity (see 12.5.1 Link semantics).
11.3. Invoking Web Service Operations
Web Services provided by partners (see Partner Link Types, Partner Links, and Endpoint References) can be used to perform work in a WS-BPEL business process. Invoking an operation on such a service is a basic activity. Recall that such an operation can be a synchronous request/response or an asynchronous one-way operation. WS-BPEL uses the same basic syntax for both with some additional options for the synchronous case.
An asynchronous invocation requires only the input variable of the operation because it does not expect a response as part of the operation (see Providing Web Service Operations). A synchronous invocation requires both an input variable and an output variable. Note however that if a WSDL message definition does not contain any parts then the associated variable attribute, inputVariable or outputVariable, MAY be omitted. One or more correlation sets can be specified to correlate the business process instance with a stateful service at the partner’s side (see Correlation). However, these attributes are both syntactically optional since they are absolutely required only in executable processes. Note however that if a WSDL message definition does not contain any parts then the variable attribute MAY be omitted.
In the case of a synchronous invocation, the operation might return a WSDL fault message. This results in a WS-BPEL fault. Such a fault can be caught locally by the activity, and in this case the specified activity will be performed. If a fault is not caught locally by the activity it is thrown to the scope that encloses the activity (see Scopes and Fault Handlers).
Note that a WSDL fault is identified in WS-BPEL by a qualified name formed by the target namespace of the corresponding portType and the fault name. This uniform naming mechanism must be followed even though it does not accurately match WSDL’s faultnaming model. WSDL 1.1 does not require that fault names be unique within the namespace where the service operation is defined. In WSDL 1.1 it is necessary to specify a portType name, an operation name, and the fault name to uniquely identify a fault. This limits the ability to use fault-handling mechanisms to deal with invocation faults.
BPEL faults are defined exclusively in terms of a fault name and optional fault data. This means, for example, that if a fault is generated from a messaging activity (as opposed to the throw activity or a system fault) no record will be made in the fault of the portType or operation the message activity was using when the fault was received. A consequence of this model is that all faults sharing a common name, defined in the same namespace and sharing the same data type (or lack there of) are indistinguishable in WS-BPEL. Faults of a particular fault name MAY be associated with multiple variable types and the <catch> construct in WS-BPEL facilitates differentiation of faults with different message / variable types of the same fault name. For details regarding the <faultHandlers> and <catch>, please see section "Fault Handlers".
Implementer's Note: WS-BPEL treats faults based on abstract WSDL 1.1 operation definitions, without reference to binding details. Normally, when sending or receiving a fault, a WS-BPEL process only deals with the fault information in the abstract fault message and a WSDL 1.1 binding is required to transform the abstract fault message data to or from specific communication media. In the case of SOAP bindings this would mean providing transformation between abstract fault message data and the sub elements of of the SOAP Fault element, namely the faultcode, faultstring, faultactor and detail elements. However the WSDL 1.1 standard SOAP binding explicitly precludes mapping any information from an abstract fault message to a SOAP Fault other than the contents of the detail element. In other words, there is no standard way to relate the faultcode, faultstring and faultactor sub-elements of a SOAP Fault element to data visible to a WS-BPEL process. This specification does not provide a resolution for this problem.
Finally, an activity can be associated with another activity that acts as its compensation action. This compensation handler can be invoked either explicitly or by the default compensation handler of the enclosing scope (see Scopes and Compensation Handlers).
Semantically, the specification of local fault and/or compensation handlers is equivalent to the presence of an implicit <scope> activity immediately enclosing the <invoke> activity providing those handlers. The implicit <scope> activity assumes the name of the <invoke> activity it encloses, its suppressJoinFailure attribute, its join condition, as well as its link sources and targets. For example, the following:
<invoke name="purchase" suppressJoinFailure="yes" partnerLink="Seller" portType="SP:Purchasing" operation="SyncPurchase" inputVariable="sendPO" outputVariable="getResponse"> <targets> <target linkName="linkA"/></targets>
<sources><source linkName="linkB">
<transitionCondition> ... </transitionCondition></source>
</sources>
<compensationHandler> <invoke partnerLink="Seller" portType="SP:Purchasing" operation="CancelPurchase" inputVariable="getResponse" outputVariable="getConfirmation"> </compensationHandler></invoke>
is equivalent to:
<scope name"purchase" suppressJoinFailure="yes" > <targets> <target linkName="linkA"/> </targets><sources>
<source linkName="linkB"> <transitionCondition> ... </transitionCondition></source>
</sources> <compensationHandler> <invoke partnerLink="Seller" portType="SP:Purchasing" operation="CancelPurchase" inputVariable="getResponse" outputVariable="getConfirmation"> </compensationHandler> <invoke name="purchase" suppressJoinFailure="no" partnerLink="Seller" portType="SP:Purchasing" operation="SyncPurchase" inputVariable="sendPO" outputVariable="getResponse"/></scope>
The syntax of the invoke activity is summarized below.
<invoke partnerLink="ncname" portType="qname"? operation="ncname"
inputVariable="ncname"? outputVariable="ncname"?
standard-attributes>
standard-elements<correlations>?
<correlation set="ncname" initiate="yes|no"?
pattern="in|out|out-in"/>+
</correlations>
<catch faultName=“qname”? faultVariable="ncname"? faultMessageType="qname"? faultElement="qname"?>*
activity
</catch>
<catchAll>?
activity
</catchAll>
<compensationHandler>?
activity
</compensationHandler><toPart part="ncname" fromVariable="ncname"/>*<fromPart part="ncname" toVariable="ncname"/>*</invoke>
See Correlation for an explanation of the correlation semantics. The following example shows an invocation with a nested compensation handler. Other examples are shown throughout the specification.
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="SyncPurchase"
inputVariable="sendPO"
outputVariable="getResponse">
<compensationHandler>
<invoke partnerLink="Seller" portType="SP:Purchasing"
operation="CancelPurchase"
inputVariable="getResponse"
outputVariable="getConfirmation">
</compensationHandler>
</invoke>
If the WSDL operation used to send and/or receive a message in an invoke activity is defined as a message containing exactly one part which itself is defined using an element then a BPEL variable of the same element type as used to define the part MAY be submitted directly to the invoke activity. The result of submitting a BPEL variable in the previously defined circumstance MUST be the equivalent of declaring an anonymous temporary WSDL message variable based on the associated WSDL message type. In the case of an inputVariable the value of the submitted BPEL variable will be used to set the value of the part in the anonymous temporary WSDL message variable. In the case of an outputVariable the value of the received part in the temporary WSDL message variable will be used to set the value of the submitted BPEL variable.
<toPart> elements provide another short cut that makes it easier to create outgoing multi-part WSDL messages from the contents of BPEL variables. The inputVariable attribute MUST NOT be used on an Invoke activity that also contains a <toPart> element. The <toPart> elements, as a group, act as a single virtual assign where each <toPart> is turned into a copy in the virtual assign. The destination of all the copies is an anonymous temporary WSDL variable, of the type specified by the relevant WSDL operation, which will then be used to send the actual message created by the virtual assign. Each <toPart> is turned into a copy in which data from the variable indicated in the “fromVariable” attribute is copied into the part of the anonymous temporary WSDL variable referenced in the “part” attribute of the <toPart> element.
The virtual assign MUST follow the same semantics and use the same faults as a real assign. When this mechanism is used in an Invoke, it is not required that there be a <toPart> for every part in the WSDL message definition, nor is the order in which parts are specified relevant. Parts not explicitly represented by <toPart> elements result in empty parts in the target anonymous WSDL variable used by the <invoke> activity.
<fromPart> elements are a similar short cut to <toPart> elements, but in the inverse. <fromPart> elements are used to pull data out of an incoming multi-part WSDL message and place it into individual BPEL variables. The outputVariable attribute MUST NOT be used on an Invoke activity that also contains a <fromPart> element. The <fromPart> elements, as a group, act as a single virtual assign. When a WSDL message is received on an <invoke> activity that uses <fromPart> the message is placed in an anonymous temporary WSDL variable, of the type specified by the relevant WSDL operation. The <fromPart> elements are then gathered together to form a single virtual assign where each <fromPart> is turned into a copy. Each <fromPart> is turned into a copy in which the data at the part of the anonymous temporary WSDL variable referenced in the <fromPart> is copied into the BPEL variable indicated in the “toVariable” attribute. The virtual assign MUST follow the same semantics and use the same faults as a real assign. When this mechanism is used in an Invoke, it is not required that there be a <fromPart> for every part in the WSDL message definition, nor is the order in which parts are specified relevant. Parts not explicitly represented by <fromPart> elements are simply not copied from the anonymous WSDL variable to a BPEL variables.
A single <invoke> can contain any combination of <toPart> elements, <fromPart> elements, outputVariable and inputVariable with the exception, as previously specified, that if <toPart> elements are used then the inputVariable attribute cannot be used and if <fromPart> elements are used then the outVariable attribute cannot be used. The virtual assign created as a consequence of the use of input or output elements occurs as part of the scope of the <invoke> activity and therefore any faults that are thrown can be caught by the invoke’s inline fault handler. Also note that it is legal to use <toPart>/<fromPart> with WSDL messages that only have a single part.
If an invoke activity is used on a partnerLink whose partnerRole endpoint reference is not initialized then a bpws:uninitializedPartnerRole fault MUST be thrown.
11.4. Providing Web Service Operations
A business process provides services to its partners through receive activities and corresponding reply activities. A receive activity specifies the partner link that contains the myRole used to receive messages, the port type (optional) and operation that it expects the partner to invoke. The value of the partnerRole in the partner link is not used when processing a receive activity. In addition, it may specify a variable, using the variable attribute, that is to be used to receive the message data received. However, this attribute is syntactically optional since it is absolutely required only in executable processes. An alternative to the variable attribute are <fromPart> elements. The syntax and semantics of the <fromPart> elements as used on the receive activity are the same as specified in section 11.3 for the invoke activity. This includes the restriction that if <fromPart> elements are used on a receive activity then the variable attribute MUST NOT be used on the same activity.
In addition, receive activities play a role in the lifecycle of a business process. The only way to instantiate a business process in WS-BPEL is to annotate a receive activity with the createInstance attribute set to "yes" (see Pick for a variant). The default value of this attribute is "no". A "start activity" is a receive/pick activity that is annotated with a createInstance="yes" attribute. NO other "non-start activities" but scope, flow, sequence or empty activities may potentially be performed prior to or simultaneously with a "start activity". The logical order of performing activities is determined by static analysis.
It is permissible to have multiple start activities. As specified in section 6.5, the initial start activity must complete execution before any other start activities are allowed to execute. In this case the intent is to express the possibility that any one of a set of required inbound messages can create the process instance because the order in which these messages arrive cannot be predicted. If a process has multiple start activities then all such activities MUST share at least one common correlation set and all correlation sets defined on all the activities MUST be set to "join" (see Correlation). Compliant implementations MUST ensure that only one of the inbound messages that will match to a single process instance actually instantiates the business process (usually the first one to arrive, but this is implementation dependent). The other incoming messages in the concurrent initial set MUST be delivered to the corresponding receive activities in the already created instance.
The following example is illegal, since assign activity cannot be a start activity:
<flow>
<receive ... createInstance="yes" />
<assign ... />
</flow>
The following example is legal, since the assign activity will not be performed prior to or simultaneously with the receive activity:
<flow>
<links>
<link name="RecvToAssign"/>
</links>
<sequence>
<receive ... createInstance="yes">
<sources> <source linkName="RecvToAssign" /> <sources>
</receive>
...
</sequence>
<sequence>
<assign>
<targets> <target linkName="RecvToAssign" /> </targets>
...
</assign>
</sequence>
</flow>
If the WSDL operation used to receive or send a message in a request or a reply activity is defined as a message containing exactly one part which itself is defined using an element then a BPEL variable of the same element type as used to define the part MAY be submitted directly to the request/reply activity. The result of submitting a BPEL variable in the previously defined circumstance MUST be the equivalent of declaring an anonymous temporary WSDL message variable based on the associated WSDL message type. In the case of a receive activity, the incoming part’s value will be used to set the value of the submitted BPEL variable. In the case of a reply activity the value of the submitted BPEL variable will be used to set the value of the part in the anonymous temporary WSDL message variable that is sent out. In the case of a reply that is sending a fault the same logic applies but using a fault name rather than an operation name. Aletrnatively, it is possible to use <fromPart> elements in a receive activity to indicate how the data from a received message is to be directly copied to BPEL variables from a corresponding anonymous WSDL message variable. Similarly, in the case of a reply activity, <toPart> elements may be used to have data from BPEL variables directly copied into an anonymous WSDL message used by the reply activity.
A business process instance MUST NOT simultaneously enable two or more receive activities for the same partnerLink, portType, operation and correlation set(s). Note that receive is a blocking activity in the sense that it will not complete until a matching message is received by the process instance. The semantics of a process in which two or more receive actions for the same partnerLink, portType, operation and correlation set(s) may be simultaneously enabled is undefined. For the purposes of this constraint, an onMessage clause in a pick and an onEvent event handler are equivalent to a receive (see Pick and Message Events).
It is worth pointing out that race conditions may occur in business process execution. Messages that target a particular process instance may arrive before the corresponding receive activity is started. For example, it is perfectly reasonable to model a process that receives a series of messages in a while loop where all the messages use the same correlation. At run time, the messages will arrive independent of the iterations of the loop. But the fact that the correlation is already initiated should enable the runtime engine and messaging platform to recognize that these messages are correlated to the process instance and handle those messages appropriately. For another example, a process may invoke a remote service, initiate a correlation set for an expected callback message, and the callback message may arrive before the corresponding receive activity is started for a variety of reasons. The correlation data in the arriving message should enable the engine to recognize the message is targeted for this process instance and handle it appropriately. Process engines may employ different mechanisms to handle such race conditions. This specification does not mandate any specific mechanism. For the purposes of handling race conditions, an onMessage clause in a pick and an onMessage event handler are equivalent to a receive (see Pick and Message Events).
<receive partnerLink="ncname" portType="qname"? operation="ncname"
variable="ncname"? createInstance="yes|no"?
messageExchange="ncname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?/>+
</correlations> <fromPart part="ncname" toVariable="ncname"/>*
</receive>
A reply activity is used to send a response to a request previously accepted through a receive activity. Such responses are only meaningful for synchronous interactions. An asynchronous response is always sent by invoking the corresponding one-way operation on the partner link. A reply activity may specify a variable that contains the message data to be sent in reply. However, this attribute is syntactically optional since it is absolutely required only in executable processes. Note however that if a WSDL message definition does not contain any parts then the variable attribute MAY be omitted. An alternative to the variable attribute are <toPart> elements. The syntax and semantics of the <toPart> elements as used on the reply activity are the same as specified in section 11.3 for the invoke activity. This includes the restriction that if <toPart> elements are used on a receive activity then the variable attribute MUST NOT be used on the same activity.
The correlation between a request and the corresponding reply is based on the constraint that more than one outstanding synchronous request from a specific partner link for a particular portType, operation and correlation set(s) MUST NOT be outstanding simultaneously. The semantics of a process in which this constraint is violated is undefined. For the purposes of this constraint, an onMessage clause in a pick is equivalent to a receive (see Pick). Moreover, a reply activity must always be preceded by a receive activity for the same partner link, portType and (request/response) operation, such that no reply has been sent for that receive activity. The semantics of a process in which this constraint is violated is undefined.
<reply partnerLink="ncname" portType="qname"? operation="ncname"
variable="ncname"? faultName="qname"?
messageExchange="ncname"?
standard-attributes>
standard-elements
<correlations>?
<correlation set="ncname" initiate="yes|no"?/>+
</correlations> <toPart part="ncname" fromVariable="ncname"/>*
</reply>
Note that the <reply> activity corresponding to a given
request has two potential forms. If the response to the request is normal, the faultName attribute
is not used and the variable attribute, when present, will indicate a variable of the normal
response message type. If, on the other hand, the response indicates a fault,
the faultName attribute is used and the variable attribute, when present, will
indicate a variable of the message type for the corresponding fault. Observe
that WS-BPEL treats faults based on abstract WSDL 1.1 operation definitions,
without reference to binding details. This limits the ability of a
WS-BPEL process to determine the information transmitted when faults are
returned over a SOAP binding. We refer to the Implementer’s Note in
Section 11.3 for additional details.
The optional messageExchange attribute is used to associate a
<reply> activity with an inbound message activity, such as, <receive>,
<onMessage> and <onEvent>, when there are multiple
simultaneously incomplete inbound message activities which requires a reply
message to complete.
A reply activity is associated with a inbound message activity based on the tuple - partnerLink, operation, and messageExchange. The value defined in messageExchange is scoped to the combination of partnerLink and operation. That is, it is legal to use the same messageExchange value in multiple simultaneously incomplete receive activities so long as the combination of partnerLink and operation on the receives are all different from each other. An incomplete inbound message activity describes the state of a BPEL process from the point that a request/response receive activity starts execution until its associated reply begins execution.
If there should ever be multiple simultaneous incomplete inbound message activities which have the same partnerLink, operation and messageExchange tuple then the bpws:conflictingRequest fault MUST be thrown within the BPEL process on the conflicting inbound message activities subsequent to the execution of the successful incomplete receive.
If a reply activity cannot be associated with an incomplete receive activity by matching the tuples and this error situation is not caught during static analysis, then bpws:missingRequest fault MUST be thrown within the BPEL process on the reply activity. Because conflicting requests should have been rejected at the time inbound message activity is executed, there cannot be more than one corresponding inbound message activity at the time <reply> is executed.
If the messageExchange attribute is not specified on a receive then its value is taken to be empty. For matching purposes two empty messageExchange values with the same partnerLink and operation values are said to match. Empty value does not match with other non-empty values.
11.5. Updating Variable Contents
Variable update occurs through the assignment activity, which is described in Assignment.
11.6. Signaling Faults
The throw activity can be used when a business process needs to signal an internal fault explicitly. Every fault is required to have a globally unique QName. The throw activity is required to provide such a name for the fault and can optionally provide a variable of data that provides further information about the fault. A fault handler can use such data to analyze and handle the fault and also to populate any fault messages that need to be sent to other services.
WS-BPEL does not require fault names to be defined prior to their use in a throw element. An application or process-specific fault name can be directly used by using an appropriate QName as the value of the faultName attribute and providing a variable with the fault data if required. This provides a very lightweight mechanism to introduce application-specific faults. The throw activity MAY be used to throw faults defined by this specification.
<throw faultName="qname" faultVariable="ncname"? standard-attributes>
standard-elements
</throw>
A simple example of a throw activity that does not provide a variable of fault data is:
<throw xmlns:FLT="http://example.com/faults" faultName="FLT:OutOfStock"/>
11.7. Waiting
The wait activity allows a business process to specify a delay for a certain period of time or until a certain deadline is reached (see Expressions for the grammar of duration expressions and deadline expressions).
<wait standard-attributes>
standard-elements ( <for expressionLanguage="anyURI"?>duration-expr</for> | <until expressionLanguage="anyURI"?>deadline-expr</until> )
</wait>
A typical use of this activity is to invoke an operation at a certain time (in this case a constant, but more typically an expression dependent on process state):
<sequence>
<wait><until>'2002-12-24T18:00+01:00'</until></wait>
<invoke partnerLink="CallServer" portType="AutomaticPhoneCall"
operation="TextToSpeech"
inputVariable="seasonalGreeting">
</invoke>
</sequence>
11.8. Doing Nothing
There is often a need to use an activity that does nothing, for example when a fault needs to be caught and suppressed. The empty activity is used for this purpose. The syntax is obvious and minimal.
<empty standard-attributes>
standard-elements
</empty>
11.9 Extension Activity
New activities can be introduced for use in BPEL by placing them inside of the extensionActivity element. The contents of an extensionActivity element MUST be a single element that MUST make available BPEL's standard-attributes and standard-elements. If the element contained within the