Proposal for a WSRF Primer

[Tim Banks <tim_banks@uk.ibm.com>]

I've loaded an outline of what I envisage could be developed into a Primer
for WSRF here:
http://www.oasis-open.org/apps/org/workgroup/wsrf/download.php/9440  and
attached it to this email as html.

The idea of the Primer is really very simple - here's the gist of it:


      The  ‘Primer’  will  be  an introduction to the Web Services Resource
      Framework  (WSRF)  Specifications – a first source of information for
      those  new to the specifications and an explanation of why things are
      the  way  they  are.  It  is,  therefore, aimed at a wide audience of
      architects and developers, implementers and users. No prior knowledge
      of Web Services or the Framework will be assumed.

      What  is needed is to explain the existing landscape of Web Services,
      the  work on which WSRF builds, and the requirements which create the
      need  for  each  component  of  the specifications and to give simple
      examples  of  the  way  they  are  used  without  assuming background
      knowledge.

      Also,  since there are several specifications in the WSRF collection,
      it’s  useful  to  newcomers to have all of the material summarised in
      one document.


Hopefully we can dovetail this into Alan's AppNotes idea (outlined here:
http://www.oasis-open.org/archives/wsrf/200408/msg00000.html) which deals
with applications of the specs.  Comments are extremely welcome.

(See attached file: WSRF_Primer_Outline[1].htm)

Regards, Tim Banks
IBM TP Architecture & Technology. Hursley, UK.
Phone: External +44 1962 815639, Internal 245639

Title: OGSA primer

Web Services Resource Framework (WSRF)
Primer Proposal

The ‘Primer’ will be an introduction to the Web Services Resource Framework (WSRF) Specifications – a first source of information for those new to the specifications and an explanation of why things are the way they are. It is, therefore, aimed at a wide audience of architects and developers, implementers and users. No prior knowledge of Web Services or the Framework will be assumed.

What is needed is to explain the existing landscape of Web Services, the work on which WSRF builds, and the requirements which create the need for each component of the specifications and to give simple examples of the way they are used without assuming background knowledge.

Also, since there are several specifications in the WSRF collection, it’s useful to newcomers to have all of the material summarised in one document.

 

The proposed outline contents are shown below.

1.      About this Primer

1.1.   Who should read it

2.      Web Services Background

2.1.   [TB1] What is a Web Service?

This should include examples of services which demonstrate the range of application and the requirement for WSRF.

 

è  Passing of reference parameters to a requestor for use on Web service calls

è  Management of distributed systems

2.2.   Web service Implementation

Although we aren’t concerned with how Web Services are actually implemented, a good specification enables factoring of implementation.

2.2.1.      Application vs Infrastructure

Explains the separation of concerns between:

è  The WSDL description of Web Service interaction and the service which implements it.

è  The infrastructure which locates resources.

2.2.2.      Interface composition

This describes the advantages of the portType extension which allows:

è  Use of common WSDL descriptions

è  Factoring of service implementation.

2.3.   Composition of Web service specifications

How WSRF combines with other WS standards.

2.4.   Addressing Web Services

This section references and summarises approaches to addressing and the capabilities required by WSRF.

3.      Introducing Stateful Resources

An explanation of Terms, some taken from the ‘Modeling Stateful Resources’, and ‘WS Resource’ papers.

è  A stateless service implements message exchanges with no access or use of information not contained in the input message. A simple example is a service that compresses and decompresses documents, where the documents are provided in the message exchanges with the service.

è  A conversational service implements a series of operations such that the result of one operation depends on a prior operation and/or prepares for a subsequent operation. The service uses each message in a logical stream of messages to determine the processing behavior of the service. The behavior of a given operation is based on processing preceding messages in the logical sequence. Many interactive Web sites implement this pattern through use of HTTP sessions and cookies.

è  A service that acts upon stateful resources

è  …More terms from the WS Resource paper

 

3.1.   What are ‘resources’?

3.2.   What makes Services ‘stateful’?

The OGSI Primer has material that covers this point.

4.      Requirements

First the high-level, then the low level, explaining the connection and how these are related to the specifications.

4.1.   Large scale distributed applications

4.1.1.      Computational Grid Systems

The background & OGSI. The requirements for integration, limited resource lifetime, Service Groups, Introspection, stabilitiy of identification (Locators, handles), etc.

There is material in the OGSI Primer that will serve.

4.1.2.      Distributed systems management

WSDM requirements for flexible resource control via get/set.

4.1.3.      Distributed information systems

OGSA –DAI might provide an example.

4.2.   Low level requirements

These attributes and requirements are characteristic of distributed architectures. This section explains which parts of WSRF deal with them

4.2.1.      WS Resource Lifecycle

Creation is domain/application specific. Destruction is described by WS-RL.

4.2.2.      Finding WS Resources

Location can be implemented by derivatives of WS-SG.

4.2.3.      Identification

What is identification?

4.2.4.      Construction of messages

Encoding of disambiguators which enables separation of identification from application concerns.

4.2.5.      Structured Faults

A summary of the advantages represented by WS-BaseFaults

4.2.6.      Renewability of Addresses

?

4.2.7.      Accessing state

Common requirements for get/set access or messages, described by WS-RP

4.2.8.      Notification

A description of the requirement and a pointer to WS-N.

4.2.9.      Introspection

?

5.      Relationship to non-WSRF Web services

Describes other approaches to resource identification, and how they can be used in conjunction with WSRF. This should answer questions like:

5.1.   WS-Resource Relationship Cardinality and the ‘singleton pattern’

5.2.   Using explicit parameters

Some examples of explicit parameters and how they are used in conjunction with WSRF disambiguators.

5.3.   UDDI

Relationship of UDDI to WS-SG

5.4.   Relationship to OGSI

It might be helpful to include nuggets from the paper “From OGSI to WS-Resource Framework: Refactoring and Evolution”:

6.      Describing WS Resources

6.1.   Web Services Description Language (WSDL)

6.2.   Resource Properties document

Properties are a way to express the state of a WS Resource, give it semantics, generate access messages to query and update the properties

6.2.1.      The Structure of a Properties Document

7.      Resource Property  Operations

A summary of the styles of interaction and their semantics.

8.      Finding Services: ServiceGroups and Registries

The OGSI Primer has this material

8.1.   The Registry Interfaces

8.1.1.      The purpose of registries in OGSA

8.1.2.      OGSI Support for Service Registries

8.1.3.      Factory and Instance Registration

8.1.4.      Making Discoveries

8.2.   Grouping services: The ServiceGroup portType

8.2.1.      The membershipContentRule

8.2.2.      The entries

8.3.   Proxies for ServiceGroup members: The ServiceGroupEntry

8.3.1.      The memberServiceLocator

8.3.2.      The content

8.4.   Managing ServiceGroup membership: The ServiceGroupRegistration portType

8.4.1.      The add Operation

8.4.2.      The remove Operation

 

9.      Glossary of Terminology

For example:

·    Stateful resource:

Something which

è  Has a specific set of state data expressible as an XML document

è  Has a well-defined lifecycle

è  Is known to, and acted upon, by one or more Web services.

 

Term	Meaning	Bookmark
WS Resource		WS_Resource

 

---

 [TB1] [TB1]The scope of  this section (and the next two ) is essentially the introduction from the paper ‘Modeling Stateful Resources with Web Services’, but a) it will be updated to match the terminology  that has evolved b) more examples and fewer references will be used.