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Subject: Re: [wsbpel] Issue - 229 - Fault handling and compensation handlingallows selective compensation of child scopes
Hi, Alexandre and others, I do support opening this issue. On the other hand, I am not sure an error needs to be raised when reverse order invariant is not observed. The reverse order is the default compensation order, NOT the only compensation order. Instead, we can issue a warning (both compile time and runtime). Even though we decided not to add a "reversable" flag to <scope> construct in Issue 10 for simplicity, scopes are often introduced to a process definition in reality which actually have not significance in the context of compensation (e.g. just to introduce local partnerLink, perform some non-business tasks that cannot and need not be be compensated). Those scopes should be safe to be ignore in the context of compensation. Also, while there may be a logical order of dependence of forward-work among scopes, a logical order may not necessarily exist in the backward-work among scopes. For example, scope-A has two sub-scopes: one for PO creation, one for ShippingOrder creation. Creation of ShippingOrder depends on the PO-id from PO creation. However, when we want to cancellation of both PO and SO during compensation, the cancellation of PO does not necessarily depend on the cancellation of SO (depending on the argreed procotols among customer and vendors and shippers). In fact, one may cancel PO and SO in parallel. Thanks! Regards, Alex Yiu Alexandre Alves wrote: Hi Alastair, Isn't it already possible to break this reverse order invariant by having the user explicitly compensate named scopes: <scope name="root"> <faultHandlers> <catchAll> <compensate scope="a"> <compensate scope="b"> <!-- does not follow reverse order --> </catchAll> </faultHandlers> <compensationHandler> <compensate scope="a"> </compensationHandler> <sequence> <scope name="a"> ... </scope> <scope name="b"> ... </scope> <scope name="c"> ... </scope> </sequence> If so, it seems to me that parameterized compensation handlers are already needed. And this scenario is not very different from the proposed solution n. 4: <catchAll> <compensate scope="a"> <compensate /> <!-- default compensation --> </catchAll> I do think we should open this issue. I would volunteer that one possible solution to this problem could be to (conditionally) raise a fault if the reverse order invariant is broken. Best regards, Alexandre -----Original Message----- From: Green, Alastair J. [mailto:Alastair.Green@choreology.com] Sent: Tuesday, September 27, 2005 10:48 AM To: chris.keller@active-endpoints.com; Yuzo Fujishima; wsbpel@lists.oasis-open.org Subject: RE: [wsbpel] Issue - 229 - Fault handling and compensation handling allows selective compensation of child scopes I think I disagree with the premise of this issue, that a change is needed in this area. The default behaviour, as I recall, is that the compensation handlers of children will be processed in reverse order of scope processing. This facility allows an override, to permit selective and partial reversals. If this is removed then the process designer is forced to create shared state to parameterize compensation handlers such that they know the context in which they have been called, which is more fragile, error-prone and difficult to code than allowing parental dictation. Unless I am missing something, there is no compulsion to use this feature. It seems like a useful facility, and a case of caveat emptor. Alastair -----Original Message----- From: Chris Keller [mailto:chris.keller@active-endpoints.com] Sent: 27 September 2005 16:45 To: 'Yuzo Fujishima'; wsbpel@lists.oasis-open.org Subject: RE: [wsbpel] Issue - 229 - Fault handling and compensation handling allows selective compensation of child scopes Hi Yuzo, Interesting suggestion. I have one question on your option. If a user creates a catch block for a fault or a compensation handler that doesn't use <compensate/> will compensation handling of child scopes be done before or after the user's code or not at all? One disadvantage of the suggestion is that if you have invokes not in a scope of their own (or declaring a compensation handler of its own) then the user may need to interleave its compensation with that of child scopes. That requires the user to dictate the order of compensation which would be prohibited by this option. Of course we could say the user must add a compensation handler directly to the invoke itself for appropriate interleaving with child scopes, which is probably the lesser of evils. - Chris -----Original Message----- From: Yuzo Fujishima [mailto:fujishima@bc.jp.nec.com] Sent: Monday, September 26, 2005 9:32 PM To: wsbpel@lists.oasis-open.org Subject: Re: [wsbpel] Issue - 229 - Fault handling and compensation handling allows selective compensation of child scopes Chris, I would like to propose the fifth option: 5. Disallow specifying the target scope for the compensate activity. I.e., legal: <compensate/> illegal: <compensate scope="...*/> Have the compensation handler of the scope, not the caller, decide whether the compensation should be done. Rationale: I think the source of the problem is that the current specification makes the caller of the compensation handlers decide which scopes should be compensated while only each scope's compensation handler knows how and if compensation needs to be done. Yuzo ws-bpel issues list editor wrote:This issue has been added to the wsbpel issue list with a status of "received". The status will be changed to "open" if a motion to opentheissue is proposed and that motion is approved by the TC. A motioncouldalso be proposed to close it without further consideration. Otherwiseitwill remain as "received". The issues list is posted as a Technical Committee document to theOASISWSBPEL TC pages <http://www.oasis-open.org/apps/org/workgroup/wsbpel>ona regular basis. The current edition, as a TC document, is the most recent version of the document entitled ** in the "Issues" folder oftheWSBPEL TC document list <http://www.oasis-open.org/apps/org/workgroup/wsbpel/documents.php> - the next posting as a TC document will include this issue. The list editor's working copy, which will normally include an issue when it isannounced, is available at this constant URL <http://www.choreology.com/external/WS_BPEL_issues_list.html>. Issue - 229 - Fault handling and compensation handling allows selective compensation of child scopes *Status:* received *Date added:* 26 Sep 2005 *Categories:* Compensation <#category_compensation> *Date submitted:* 21 September 2005 *Submitter:* Chris Keller <mailto:chris.keller@active-endpoints.com> *Description:* Currently fault handling and compensation handlingallowsusers to selectively compensate work done by child scopes. This canleadto errors in the process especially as users change their processesovertime. In addition it does not seem to be in the spirit of the BPELfaulthandling and compensation handling model in general (as well as good modular programming practice). Take the following example: <scope name="root"> <faultHandlers> <catchAll> <compensate scope="a"> </catchAll> </faultHandlers> <compensationHandler> <compensate scope="a"> </compensationHandler> <sequence> <scope name="a"> ... </scope> <scope name="b"> ... </scope> <scope name="c"> ... </scope> </sequence> If a fault is caused by scope "c" the catchAll will only compensate"a"leaving "b" uncompensated. Let's assume programmer 1 created theprocessand didn't bother to compensate "b" since "b" at that time didn't doanyreal work. Now programmer 2 picks up that process later and adds real work and a compensation handler for it to scope "b" not realizing thatthe catchAll will not compensate "b" and that the work will not be compensated. Additionally if the real work added to scope "b" was accomplished by programmer 2 by adding a child scope "b1" to "b". Programmer 2 lookingat scope "b" may think that default compensation handling is in place and feel safe that their new work will be compensated. Not realizing that the scope "root" has selectively chosen not to compensate "b" andthereby "b1" in the process. Possible solutions: 1. After user defined fault handling and compensation handling is executed default handling will execute to compensate all other completed child scopes left uncompensated. 2. If after user defined fault handling and compensation handlingisexecuted there remains child scopes that have not beencompensatedthrow an bpws:missingCompensation exception. 3. Do nothing and say selective compensation is legal and good. And add a note that users should take care when changing business processes to ensure that user defined fault handling and compensation handling call compensate on the child scopescorrectly.4. Same as 3 with one exception after a user calls <compensate name="..."> allow them to call <compensate/> which willcompensateall remaining child scopes in the default order. This would require changing the following text at the end of section13.3.3:"Note that the <compensate/> activity in a fault or compensation handler attached to scope S causes the default-order invocationofcompensation handlers for completed scopes directly nestedwithinS. The use of this activity can be mixed with any other user-specified behavior except the explicit invocation of <compensate scope="Sx"/> for scope Sx nested directly within S. Explicit invocation of compensation for such a scope nestedwithinS disables the availability of default-order compensation, as expected." *Changes:* 26 Sep 2005 - new issue To comment on this issue (including whether it should be accepted), please follow-up to this announcement on thewsbpel@lists.oasis-open.orglist (replying to this message should automatically send your messagetothat list), or ensure the subject line as you send it *starts* "Issue-229 - [anything]" or is a reply to such a message. If you want to formally propose a resolution to an open issue, please start thesubjectline "Issue - 229 - Proposed resolution", without any Re: or similar. To add a new issue, see the issues procedures document (but theaddressfor new issue submission is the sender of this announcement). Choreology Anti virus scan completed--------------------------------------------------------------------- To unsubscribe from this mail list, you must leave the OASIS TC that generates this mail. 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