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Subject: Re: [wsbpel] Issue - 123 - Matching <reply> with <receive>
Hi, Paco, (and others),
I guess we can consolidate the text from "lifetime"/"namespace" into
"scope", if you prefer. I was just reusing those terms from on Yuzo's
original proposal.
Let me answer some of your questions and re-iterate some of points
expressed in the conf call today:
* I am NOT proposing the usage id is required. They are used only
when we need to disambiguate multiple receive.
* This usage id will NOT affect the actual existing partnerLink
behavior in anyway. It is a pure BPEL language feature, which has
ZERO effects to the underlying WSDL layer. The usage id is just a
supplementary qualifier for disambiguation.
* The key part of this proposal is try to bring the advantages of R1
and R1A under one proposal. Semantic-wise, the scope of the usage
identifier can have the following choices:
(I) per BPEL process: Similar to "R1"
(II) per partnerLink: Each partnerLink has its own namespace for
usage identifier. That is my /_CURRENT_/ proposed semantics.
* As of my current proposed semantics, "Scope"/"namespace" is per
partnerLink. That means:
o The same identifier CANNOT be used for 2 receive/reply pairs
on the same plink. That means the following is illegal.
<scope>
<partnerLink name="p1" ... />
<receive partnerLink="p1" operation="op1" usage="u1" />
<receive partnerLink="p1" operation="op1" usage="u1" />
<reply partnerLink="p1" operation="op1" usage="u1" />
<reply partnerLink="p1" operation="op1" usage="u1" />
</scope>
o The usage identifier are not shared among partnerLink. It is
legal to do the following:
<receive partnerLink="p1" operation="op1"
usage="handleCust" />
<reply partnerLink="p1" operation="op1" usage="handleCust" />
<receive partnerLink="p2" operation="op1"
usage="handleCust" />
<reply partnerLink="p2" operation="op1" usage="handleCust" />
(No matter whether p1 and p2 are declared in the same scope
or not)
From the BPEL engine viewpoint, the first receive operation
is now identified as the key tuple("p1"-"handCust", "op1",
cs). "handCust" becomes a part of supplementary name of the
partnerLInk.
* I totally agree with you that <receive> conflict / ambiguity
should not happen that commonly. However, after passing Issue 75,
I tend to think we want to make the <scope> construct as modular
as possible. So, it will be easier for us to move / copy the
<scope> around from one process to another process. A per-process
namespace (I) for the "usage" identifier is not good enough for
this _modularity_ goal.
* The <receive> conflict / ambiguity can be avoided in a large
extent by using a locally scope partnerLink without using the
"usage" identifier already. Therefore, I suggest (II) semantics
where the "usage" identifier fits as merely a supplement
identifier to a partnerLink.
* I will send a separate email to illustrate how I see locally
scoped partner can solve a majority of <receive> conflict /
ambiguity problems already.
Thanks!
Regards,
Alex Yiu
[P.S.: A third alternative semantics: (III) coincide with the same scope
which the used partnerLink is declared: that is a macro version of an
implicit declaration of "messageExchange" element in "R1B". (I think
that is what Maciej mentioned in the conf call. I said it is the current
semantics of my proposal by mistake. Sorry about that.) ]
Francisco Curbera wrote:
>
>
>Hi Alex,
>
>I like the simplicity approach that your R1B shares with R1. However, I
>don't really understand the following:
>
> Lifetime: you say the "lifetime" of an identifier is the plink. Does
> that mean that the same identifier can be used for 2 receive/reply pairs
> on the same plink - supposedly non conflicting ones? This seems to open
> the door for ambiguity or at least lack of clarity. Making ids unique
> per MEP instance is a much simpler approach. Maybe you really mean
> "scope"...
> "Namespace" (again I think this is actually "scope"): what is good about
> enabling the language so two MEP instances in different plinks can share
> the same usage id? The design looks particularly error prone,
> potentially misleading authors/consumers of process definitions to match
> receives and replies incorrectly because their usage ids match (but
> their plinks don't!). It certainly gives you flexibility but I don't
> know if the potential confusion and lack of readability makes it worth.
> I don't understand your last point about receive identification. Are you
> proposing that the usage id be required? Or that it have a runtime
> representation in messages targeted at that receive?
>
>I am really skeptical that dealing with name collisions is actually
>necessary in this case, seems to me we're trying to attack a problem that
>does not exist. The fact is that <receive> conflicts of this kind are
>probably going to be uncommon overall. Even when they happen I doubt that
>we'll see so many conflicts in a single process that you cannot deal with a
>single process-wide naming scope for MEP instance ids. The little benefit
>we can get out of the solutions proposed to deal with the id collission
>problem doesn't seem justify the additional complexity they all introduce.
>
>Paco
>
>
>
>
> Alex Yiu
> <alex.yiu@oracle. To: ygoland@bea.com
> com> cc: Satish Thatte <satisht@Microsoft.com>, Francisco Curbera/Watson/IBM@IBMUS,
> "Eckenfels. Bernd" <B.Eckenfels@seeburger.de>, wsbpel@lists.oasis-open.org, Alex Yiu
> 08/03/2004 11:02 <alex.yiu@oracle.com>
> PM Subject: Re: [wsbpel] Issue - 123 - Matching <reply> with <receive>
>
>
>
>
>
>
>Hi, all,
>
>After reading all the emails on this thread, I guess "R1" and "R1A" have
>its own pros and cons.
>
>I am think out loud again here to try to come up with a third proposal (
>"R1B") to address both simplicity and clarity of scope.
>
>(This is not my super firm position. The opinions polled split as 50-50 so
>far. This is just yet another "thinking-out-loud" attempt to merge two
>solutions into one):
>
>Proposal of "R1B":
> Syntax-wise, it is similar to "R1". Except I would suggest to rename
> to something like "usage" or "plinkUsage". E.g.:
> <receive partnerLink="plink1" usage="handleCustomer" ...>
> ...
> <receive partnerLink="plink1" usage="handlerShipper" ...>
> ...
> <reply partnerLink="plink1" usage="handlerCustomer" ...>
> ...
> <reply partnerLink="plink1" usage="handlerShipper" ...>
> The identifier used in the attribute does NOT need to be declared
> explicity in a scope beforehand. The identifier is declared
> implicitly in a sense. (This addresses the need of simplicity.)
> Semantics of the identifier used in the "usage" attribute:
> Lifetime: The lifetime of the "usage" identifier shares the the
> lifetime of the partnerLink used in the operation. This
> addresses both the need of clarity of lifetime and imposes a
> tighter control and make sure the lifetime of the identifier is
> sync with the lifetime of the partnerLink.
> Namespace: The namespace of the identifier is PER partnerLink.
> For examples: (all of the following are using the same
> operation and CS)
> <receive partnerLink="plink1" usage="handleCustomer" .../>
> <receive partnerLink="plink1" usage="handlerShipper" .../>
> These two receive operations do NOT collide.
> <receive partnerLink="plink1" usage="handleCustomer" .../>
> <receive partnerLink="plink2" usage="handlerCustomer" .../>
> These two receive operations do NOT collide.
> <receive partnerLink="plink1" usage="handleCustomer" .../>
> <receive partnerLink="plink1" usage="handlerCustomer" .../>
> These two receive operations do collide. This collision
> MUST be caught by static analysis.
> This addresses name collision prevention. And, it actually
> makes even easier to avoid any name collision.
> Unique key to identify a receive operation: We continue to have
> 3 components to uniquely identify a receive:
> [a] partnerLink (+ "usage" attribute, if used)
> [b] operation
> [c] any CS (if used)
>
>I hope you guys like my proposal.
>Thanks!
>
>
>If you guys still want to read further, here is my analysis on the current
>R1 and R1A proposal:
> R1:
> Advantage: simple syntax (just one attribute)
> Disadvantage: scope of the identifier used in that attribute is
> NOT clear (i.e. leading to "unclear MEP lifetime" and "harder
> name collision prevention" in Yuzo's previous email)
> R1A:
> Advantage: scope of identifier used in that attribute is clear.
> Disvantage:
> A bit too verbose
> An odd concept introduced:
> As of current spec stands, we have 3 components to
> uniquely identify a receive: [a] partnerLink [b]
> operation [c] any CS (if used). With R1A, we now
> introduce yet one more entity ("messageExchange")
> to the formula. Its lifetime can be totally in a
> different scope compared with partnerLink or CS.
> We are making a 2 dimensional problem (two disjoint
> entities: partnerLink and CS) into 3 dimensional
> one.
> Apart from this disambiguating usage, this
> messageExchange entity does not have other usages
> and meaning. Yet, it has the naming of this board
> semantics. It may tempt vendors and customers to
> overload and extend that term signficantly in a
> totally unpredictable way.
>
>Thanks!
>
>
>
>Regards,
>Alex Yiu
>
>
>
>
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>
>
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