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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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