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Subject: Re: [wsbpel] Issue - 274 - Proposal to Vote


Title: [wsbpel] Issue 274 Proposal to Vote

Hi Mark,

I guess you would not be surprised that I still prefer detecting orphaned IMA at the end of compensationHandler. Reasons are:
  • The missingReplies error is actually resulted from the modelling mistake or unanticipated runtime failure in the child scope (which the CH is attached), not the FH of the parent scope. Fault at the CH level is more precise.

  • From section 12.4.2: "This is because their compensation handlers are still available, and therefore the execution of such scopes may continue during the execution of their compensation handlers, which can be thought of as an optional continuation of the behavior of the associated scope." I tend to interprete that the primary (normal) activity of the scope is its part #1, while the activity of the CH of that scope is its part #2. Their nature should be symmetrical in the counter-working way. If we perform certain checks in part #1, similar checks should happen in part #2.

  • The asymmetry between missingReplies and other fault (e.g. selectionFailure) concerns me. (This is the last but the most important point.) If there is a problem in the CH logic that triggers a fault (e.g. selectionFailure), it will be propagated from the CH to the corresponding compensation activity in FCTHandler (fault, compensation and termination).  If there is no fault handling around the compensation activity, the whole FCTHandler will not continue. But, now we are saying that the FCTHandler will continue until its end, if the error condition is the missingReplies fault? This asymmetry may be surprising to users. I would say it may the process more difficult to model.

Let me use one more example to illustrate my preference. If one wants to continue the logic in a FH including continuing other compensation activities, one want to add a scope

That is changing from:
---------------------------------------
<catch ... >
   <sequence>
        <compensationScope target="A" />
        <compensationScope target="B" />
        <compensationScope target="C" />
   </sequence>
</catch>
---------------------------------------
to:
---------------------------------------
<catch ... >
   <sequence>
        <scope>
            ...
            <catchAll>  <empty/> </catchAll>
            ...
            <compensationScope target="A" />
        </scope>
        <compensationScope target="B" />
        <compensationScope target="C" />
   </sequence>
</catch>
---------------------------------------

This <catchAll> will handle all kind of faults, not just missingReplies.

Again, it will allow BPEL process definition to have a finer grain of control on how to handle missingReplies fault. 

Also, **if** the work of "A", "B" and "C" are highly related to each other, I would say that it is actually more common for the process designer to prefer the compensation work stop immediately, if the compensation of "A" failed. That will avoid any propagating any strange states from "A" to "B" and "C".  That is also consistent with the design of Compensation Handler Instance Group. That is, if one instance fails within the group, other instances (not started yet) will not be attempted.


I hope I did a better convincing job this time. :-)

More thoughts?
Thanks!



Regards,
Alex Yiu



Mark Ford wrote:

In dealing with an orphaned IMA within a compensation handler, it seems to me that there are two possible resolutions. Either the compensation handler detects the orphaned IMA's and faults or the detection of orphaned IMA's is deferred to the fault handler or termination handler that invoked the compensation handler. I am in favor of the latter since it allows compensation to continue even with orphaned IMA's. There is very little that can be done with these orphaned IMA's so we may as well allow the compensation logic to proceed as best it can and defer its fault to

I have reworded my original proposal to avoid introducing any new terms as per Danny's suggestion. The approach is still the same in that the detection of an orphaned IMA is NOT made by the compensationHandler.

Add a fifth bullet to Section 12.2 which reads as follows:

No checks for orphaned IMA's are made when a compensation handler completes. The compensation handler's execution must necessarily start from within a fault or termination handler so any orphaned IMA's created by a compensation handler will be detected and handled as described in the above bullets.




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