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Subject: Re: [wsbpel] Issue 6 - Rough draft of proposal for vote
i apologize for not being more explicit to begin with but imagine the
following scenario, based on your example. to borrow a phrase, this is
based on my lay understanding of the spec, and i apologize again in
advance if this reasoning is incorrect.
- outer scope initializes and sets counter to 0.
- flow initializes.
- each of 3 scopes initializes in parallel
- the ... section of the first 2 scopes completes at the same time; the
3rd one hangs "forever," or for close enough to forever to satisfy the
forever test.
- the assigns of the first 2 scopes evaluate the "from" portion
simultaneously, yielding a value of 1.
- the "to" portions of the assign happen in some order. doeesn't matter.
now counter has miscounted, since 2 branches have completed, yet only 1
completion is "recorded."
the flow will "never" complete.
this would be solved if the leaf scopes were serializable. have some
implicit concurrency control would be the huge advantage IMO, of having
built-in N of M syntax. not that i'm necessarily advocating that
complexity, but i think that if it is a common enough use case (which i
think is really the crux of the issue) then asking people to get this
right on their own is giving them enough rope to hang themselves, as
well as giving them a boy scout knot-tying manual.
Yaron Y. Goland wrote:
> What the code implements is a 'at least N out of M'.
>
> Generally when we have N out of M scenarios (which are pretty rare,
> most of our flow + break scenarios tend to be 'first to finish') the
> goal is to make sure that at least N happens. If more than N happens
> that's o.k. too.
>
> Put another way, try to imagine a scenario where you want exactly N
> out of M. Why is 'exactly' important? Heck, what does 'exactly' even
> mean? My suspicion is that any scenario where 'at least N out of M'
> doesn't work requires either full serialization of all the code or 2PC.
>
> Just a guess,
>
> Yaron
>
> Danny van der Rijn wrote:
>
>>
>>
>> in that case, don't you have some serious concurrency issues?
>>
>> Yaron Y. Goland wrote:
>>
>> > Actually no. I just meant them as generic wrappers. I could just as
>> > easily have used sequence instead of scope.
>> >
>> > Danny van der Rijn wrote:
>> >
>> >>
>> >>
>> >> i assume that the leaf scopes are serializable and that's why
>> they're
>> >> there?
>> >>
>> >> Yaron Y. Goland wrote:
>> >>
>> >> > Below is an example of 2 out of 3, it is generalizable from
>> there.
>> >> >
>> >> > scope
>> >> > variables
>> >> > variable name="counter" type="xs:int"
>> >> > sequence
>> >> > assign
>> >> > copy
>> >> > from literal="true"
>> >> > "0"
>> >> > to
>> >> > $counter
>> >> > flow
>> >> > scope
>> >> > ...
>> >> > assign
>> >> > copy
>> >> > from
>> >> > $counter + 1
>> >> > to
>> >> > $counter
>> >> > switch
>> >> > case
>> >> > condition
>> >> > $counter >= 2
>> >> > break
>> >> > scope
>> >> > ...
>> >> > assign
>> >> > copy
>> >> > from
>> >> > $counter + 1
>> >> > to
>> >> > $counter
>> >> > switch
>> >> > case
>> >> > condition
>> >> > $counter >= 2
>> >> > break
>> >> > scope
>> >> > ...
>> >> > assign
>> >> > copy
>> >> > from
>> >> > $counter + 1
>> >> > to
>> >> > $counter
>> >> > switch
>> >> > case
>> >> > condition
>> >> > $counter >= 2
>> >> > break
>> >> >
>> >> >
>> >> > Trickovic, Ivana wrote:
>> >> >
>> >> >>
>> >> >>
>> >> >> Yaron,
>> >> >>
>> >> >> Would you illustrate how break activity could be used? How
>> does it
>> >> >> resolve problems tackled by proposals we have on table at the
>> >> moment?
>> >> >>
>> >> >> Regards,
>> >> >>
>> >> >> Ivana
>> >> >>
>> >> >> > -----Original Message-----
>> >> >> > From: Yaron Y. Goland [mailto:ygoland@bea.com]
>> >> >> > Sent: Dienstag, 14. September 2004 00:01
>> >> >> > To: Alex Yiu
>> >> >> > Cc: Trickovic, Ivana; Axel Martens; Frank Leymann; Dieter
>> >> >> > Roller; Dieter
>> >> >> > Koenig1; edwink@collaxa.com; satisht@microsoft.com;
>> >> >> > wsbpel@lists.oasis-open.org
>> >> >> > Subject: Re: [wsbpel] Issue 6 - Rough draft of proposal
>> for vote
>> >> >> >
>> >> >> >
>> >> >> > I believe that the complexity of the current proposal is well
>> >> >> > above the
>> >> >> > capabilities of what I expect to be the average BPEL
>> programmer.
>> >> >> > Completion conditions, ignorable faults, new XPATH functions,
>> >> etc.
>> >> >> > introduces a lot of complexity that I believe that average
>> BPEL
>> >> >> > programmer would not be interested in dealing with.
>> >> >> >
>> >> >> > We know from many decades of language experience that average
>> >> >> > programmers can deal with break/continue. I know from at
>> >> >> > least our own
>> >> >> > experience at BEA that users can deal with the concept of a
>> >> >> > flow where a
>> >> >> > break in the flow results in the other members of the flow
>> being
>> >> >> > terminated in the BPEL meaning of the term.
>> >> >> >
>> >> >> > Defining a break activity and specifying that if break is
>> used
>> >> in the
>> >> >> > context of flow then this means that the flow activity ends
>> >> and any
>> >> >> > uncompleted members of the flow are terminated would both fit
>> >> >> > directly
>> >> >> > into BPEL's existing syntax and semantics and I believe be
>> >> >> > simple enough
>> >> >> > that the average programmer can handle it. I would therefore
>> >> >> > offer break
>> >> >> > (and it's relative 'continue') as an alternative.
>> >> >> >
>> >> >> > Thanks,
>> >> >> >
>> >> >> > Yaron
>> >> >> >
>> >> >> > Alex Yiu wrote:
>> >> >> >
>> >> >> > >
>> >> >> > > Hi,
>> >> >> > >
>> >> >> > > Ivana, thanks for sending out this proposal.
>> >> >> > > I believe a number of us (including me) like the
>> >> >> > <completionConditon>
>> >> >> > > construct from your proposal high level speaking.
>> >> >> > >
>> >> >> > > After reading the proposal, I guess we need to work on a
>> >> number of
>> >> >> > > details. I would like to ask a few questions / mention a
>> few
>> >> >> points:
>> >> >> > >
>> >> >> > > * Minor syntax and semantics questions :
>> >> >> > > o Do we want to allow expression for branch
>> >> >> > attribute? instead
>> >> >> > > of just a constant integer?
>> >> >> > > o We may need to some minor syntax adjustment for
>> >> >> > expression
>> >> >> > > attribute because we have passed Isseu 13
>> already.
>> >> >> > > o If answers to the above question are yes, then
>> >> >> > the condition
>> >> >> > > syntax may become a choice (xsd:choice) of the
>> >> >> > following two:
>> >> >> > > <condition
>> >> >> > > >
>> >> >> expressionLanguage="anyURI"?>boolean-expression</condition>
>> >> >> > > <branchCondition
>> >> >> > > >
>> >> >> expressionLanguage="anyURI"?>integer-expression</condition>
>> >> >> > >
>> >> >> > > * About completionConditionFailure : it looks like a
>> >> >> > nice idea so
>> >> >> > > far ...
>> >> >> > >
>> >> >> > > * About the new "isCompleted()" function : I am not
>> >> >> > against this
>> >> >> > > function. But, I tend to think there are usually BPEL
>> >> >> > variables
>> >> >> > > being modifed as the execution result of a flow
>> >> >> > activity. (See the
>> >> >> > > train-or-plane-and-hotel example). Is it more typical
>> >> to have
>> >> >> > > completionCondition to be evaluated on those
>> variables?
>> >> >> > > Also, after the completion of the whole flow, it is
>> >> >> > not uncommon
>> >> >> > > for people to have logic to find out which branch is
>> >> finished
>> >> >> > > (especially when "or" is involved in the
>> condition). The
>> >> >> > > "isComplete()" function would be available only
>> within
>> >> the
>> >> >> > > completionCondition within the flow. People may get
>> >> >> > confused and
>> >> >> > > attempt to use the "isComplete()" function outside
>> >> >> > the flow. If
>> >> >> > > the completionCondition relies on variables, the same
>> >> >> logic is
>> >> >> > > applicable outside of the flow.
>> >> >> > >
>> >> >> > > * About the IgnoreFault semantics: I recall this
>> >> >> > ignoreFault idea
>> >> >> > > back to March F2F. With ignoreFault semantics, it
>> >> essentially
>> >> >> > > introduces two brand new semantics.
>> >> >> > > o It turns <flow> into a semi-<scope> like
>> construct
>> >> >> > > o It adds this new "ignoreFault" semantics: which
>> >> catches
>> >> >> > > certain fault and the catching action will not
>> >> cause
>> >> >> any
>> >> >> > > scope to be marked as faulted.
>> >> >> > >
>> >> >> > > I tend to think this "ignoreFault" functionality has
>> >> >> > quite a heavy
>> >> >> > > weight impact to <flow> and fault handling picture in
>> >> >> > BPEL. If there
>> >> >> > > is an alternative way to achieve similar business
>> >> >> > logic, I would go
>> >> >> > > for the alternative way.
>> >> >> > >
>> >> >> > > Quoted from Ivana's email:
>> >> >> > > " Not all activities must complete in order the
>> >> enclosing flow
>> >> >> > > activity to complete. The way to identify that an
>> >> >> > enclosed activity
>> >> >> > > did not complete is to propagate faults. "
>> >> >> > >
>> >> >> > > I agree with the first sentence. But, I am not sure
>> >> >> > that propagating
>> >> >> > > fault is the only way to identify an enclosed activity
>> >> did not
>> >> >> > > complete. I would rather use a scope as an activity
>> >> enclosed by
>> >> >> > > flow. If we wish to suppress any minor fault which
>> >> >> > happens during
>> >> >> > > the execution of the scope, then we can just add a
>> >> >> > fault handler. If
>> >> >> > > the fault that happen, the scope will be marked as
>> >> "faulted".
>> >> >> > >
>> >> >> > > The completeConditon can identify the "incomplete"
>> state
>> >> of the
>> >> >> > > scope by two ways:
>> >> >> > >
>> >> >> > > * completeCondition can be evaluated based on BPEL
>> >> >> > variables,
>> >> >> > > which are set to "incomplete" state by pre-flow
>> >> >> > initialization
>> >> >> > > or related fault-handler logic.
>> >> >> > > * branch-based condition will interprete a faulted
>> >> scope as
>> >> >> > > "incomplete" branch and will not count them into
>> >> >> > the required
>> >> >> > > N branches.
>> >> >> > >
>> >> >> > > This will allow us to suppress minor fault with or
>> >> without the
>> >> >> > > <completionCondition> construct. Please see the
>> >> >> > following example.
>> >> >> > > It is already legal and working today. It shows how to
>> >> suppress
>> >> >> > > "foo:barFault" without the <completeCondition>
>> construct
>> >> >> > >
>> >> >> > > <flow>
>> >> >> > > <scope name="A">
>> >> >> > > <faultHandler>
>> >> >> > > <catch faultName="foo:barFault" ... > ...
>> </catch>
>> >> >> > > </faultHandler>
>> >> >> > > <sequence>
>> >> >> > > ... <invoke name="doA" ... /> ...
>> >> >> > > </sequence>
>> >> >> > > </scope>
>> >> >> > > <scope name="B"> ... <!-- similar to A --> ...
>> </scope>
>> >> >> > > </flow>
>> >> >> > >
>> >> >> > > If the invoke of "doA" triggers "foo:barFault", the
>> >> >> > scope "A" will
>> >> >> > > be marked as faulted. On the other hand, scope "B" will
>> >> >> > be allowed
>> >> >> > > to continue and complete. After scope "B" is
>> completed, the
>> >> >> > > compensation handler of scope "B" will be installed.
>> >> And, the
>> >> >> > > overall execution of flow is still considered a normal
>> >> >> > completion.
>> >> >> > >
>> >> >> > > I hope I have illustrated we can achieve similar logic
>> >> without
>> >> >> > > introducing a new "ignoreFault" construct and
>> concept to
>> >> BPEL.
>> >> >> > >
>> >> >> > > What "completionCondition" does should be just
>> >> >> > providing a way to
>> >> >> > > pro-actively cancel/terminate other flows without
>> >> >> > waiting to them to
>> >> >> > > complete or to be faulted.
>> >> >> > >
>> >> >> > > * About "Cancel-other-flows": (Let me consolidate
>> what
>> >> I am
>> >> >> > > leaning towards so far.) We need to formal define the
>> >> >> > notion of a
>> >> >> > > " cancel-other-flows " mechanism. This mechanism is
>> >> >> > specified and
>> >> >> > > attached to <flow> construct (and future parallel
>> forEach
>> >> >> > > construct). When this mechanism is triggered by one
>> >> >> > of parallel
>> >> >> > > flows, it will cancel/terminate other parallel flows
>> >> which
>> >> >> are
>> >> >> > > still running, after the triggering flow is
>> completed.
>> >> If the
>> >> >> > > other flow activties are scope activities, the scope
>> >> will be
>> >> >> > > marked as cancelled.
>> >> >> > >
>> >> >> > > This mechanism will be triggered upon the
>> >> >> > completionCondition is
>> >> >> > > evaluated to be true.
>> >> >> > >
>> >> >> > > [Note: (a) since this mechanism is triggered by
>> >> >> > without using any
>> >> >> > > fault directly. This will again decrease the need of
>> >> >> > "ignoreFault"
>> >> >> > > construct (b) This mechanism will affect the wordings
>> >> >> > of Issue 135
>> >> >> > > to an extent.]
>> >> >> > >
>> >> >> > > [Question: again, should we enforce scope-only
>> >> activity when
>> >> >> > > completionCondition is used? I tend to say yes.]
>> >> >> > >
>> >> >> > >
>> >> >> > >
>> >> >> > > Thank you all for following and reading this email
>> thread!!!
>> >> >> > >
>> >> >> > >
>> >> >> > >
>> >> >> > > Regards,
>> >> >> > > Alex Yiu
>> >> >> > > > >
>> >> >> > >
>> >> >> > > Trickovic, Ivana wrote:
>> >> >> > >
>> >> >> > >> > >>
>> >> >> > >> Here is a proposal for the completion condition - it
>> >> >> > addresses some
>> >> >> > >> issues not tackled so far (at least not in case of
>> >> >> > >> <completeCondition>). It is a version of the proposal for
>> >> >> > completion
>> >> >> > >> condition for the bundle element. This proposal includes
>> >> >> > comments from
>> >> >> > >> many people including Frank Leymann, Dieter Koenig, Dieter
>> >> >> > Roller and
>> >> >> > >> Satish Thatte. It does not mean that they completely
>> >> support the
>> >> >> > >> proposal - they may have issues with any part of the
>> proposal.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> > >>
>> >> >> > >> Completion condition
>> >> >> > >>
>> >> >> > >> =====================
>> >> >> > >>
>> >> >> > >> The current semantics of the flow activity is that it
>> >> >> > waits for all
>> >> >> > >> concurrent activities to complete. The completion also
>> >> >> > means that an
>> >> >> > >> enclosed activity/scope may end abnormally or be skipped
>> >> (e.g. the
>> >> >> > >> join condition of the activity evaluated to false). If a
>> >> fault is
>> >> >> > >> thrown within an enclosed activity/scope and one of the
>> >> >> > local fault
>> >> >> > >> handlers catch the fault (and does not rethrow the
>> fault), the
>> >> >> > >> enclosed activity/scope will be deemed to be completed
>> >> >> > (although ended
>> >> >> > >> abnormally). If a fault is not caught by any local fault
>> >> >> > handler (or
>> >> >> > >> is rethrown) the flow activity will terminate all active
>> >> >> > concurrent
>> >> >> > >> activities and corresponding fault handler may be
>> initiated.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> A completion condition for the flow activity is needed for
>> >> >> > scenarios
>> >> >> > >> where not all concurrent activities of a flow activity
>> >> >> > must complete
>> >> >> > >> in order the flow activity to complete. Note: We are not
>> >> >> > talking about
>> >> >> > >> "successful completion" of enclosed concurrent activities
>> >> >> > because that
>> >> >> > >> would not be consistent with the semantics of the current
>> >> >> > flow activity.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> The completion condition may have different flavors,
>> such as:
>> >> >> > >>
>> >> >> > >> (1) N out of M
>> >> >> > >>
>> >> >> > >> (2) The two most important requests completed
>> >> >> > >>
>> >> >> > >> (3) A Boolean condition operating upon process variables
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Not all activities must complete in order the enclosing
>> >> >> > flow activity
>> >> >> > >> to complete. The way to identify that an enclosed activity
>> >> did not
>> >> >> > >> complete is to propagate faults. We may distinguish
>> between
>> >> severe
>> >> >> > >> faults and those that can be ignored. Severe faults
>> cause the
>> >> >> > >> enclosing flow activity (or more precisely, enclosing
>> >> scope) to
>> >> >> > >> terminate the flow activity, including all active
>> concurrent
>> >> >> > >> activities, and corresponding fault handler may be
>> >> >> > initiated. Other
>> >> >> > >> faults may be ignored - the flow activity is "informed"
>> that a
>> >> >> > >> concurrent activity did not complete but still allows
>> other
>> >> active
>> >> >> > >> concurrent activities to continue with execution.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Ignore semantics
>> >> >> > >>
>> >> >> > >> =================
>> >> >> > >>
>> >> >> > >> Faults thrown within enclosed concurrent activities/scopes
>> >> and not
>> >> >> > >> handled by local fault handlers are rethrown. Enclosing
>> >> >> > <flow> element
>> >> >> > >> decides which of these rethrown faults can be ignored.
>> This
>> >> new
>> >> >> > >> "ignore" semantics should be part of the completion
>> >> condition and
>> >> >> > >> should apply to all enclosed activities. This new
>> >> >> > semantics does not
>> >> >> > >> introduce a new fault handling mechanism. It is needed for
>> >> >> > identifying
>> >> >> > >> how many of the enclosed activities failed.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> > >>
>> >> >> > >> Proposed syntax
>> >> >> > >>
>> >> >> > >> ================
>> >> >> > >>
>> >> >> > >> <flow standard-attributes>
>> >> >> > >>
>> >> >> > >> standard-elements
>> >> >> > >>
>> >> >> > >> <completionCondition/>?
>> >> >> > >>
>> >> >> > >> <links>?
>> >> >> > >>
>> >> >> > >> <link name="ncname">+
>> >> >> > >>
>> >> >> > >> </links>
>> >> >> > >>
>> >> >> > >> activity+
>> >> >> > >>
>> >> >> > >> </flow>
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> <completionCondition>
>> >> >> > >>
>> >> >> > >> <conditions branch="xsd:integer"?
>> >> >> > >>
>> >> >> > >> expression=xpath?/>?
>> >> >> > >>
>> >> >> > >> <ignoreFaults>?
>> >> >> > >>
>> >> >> > >> <fault name="qname"? value="ncname"?/>*
>> >> >> > >>
>> >> >> > >> <ignoreAll/>?
>> >> >> > >>
>> >> >> > >> </ignoreFaults>
>> >> >> > >>
>> >> >> > >> </completionCondition>
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Attribute branch is used to specify a condition of flavor
>> >> >> > "wait for
>> >> >> > >> /N/ out of /M/ activities to complete", or more precisely
>> >> value N.
>> >> >> > >> Attribute expression is used to specify a Boolean
>> >> >> > condition operating
>> >> >> > >> upon process variables or a condition of flavor "the
>> two most
>> >> >> > >> important requests completed".
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Both conditions ( branch and expression) may be specified
>> >> >> > at the same
>> >> >> > >> time. They will be checked when one instance of the scope
>> >> activity
>> >> >> > >> reaches the end. If at least one condition evaluates to
>> >> true all
>> >> >> > >> active instances will be terminated.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Element <ignoreFaults> specifies faults that may be
>> >> >> > ignored. Element
>> >> >> > >> fault is used to specify a fault which may be ignored
>> >> >> > (fault name and
>> >> >> > >> fault data may be specified). Element <ignoreAll> would
>> >> >> > mean that all
>> >> >> > >> faults thrown/rethrown by any concurrent activity/scope
>> may be
>> >> >> > >> ignored. If this element is specified <fault> element must
>> >> >> > be omitted.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Completion condition failure
>> >> >> > >>
>> >> >> > >> =============================
>> >> >> > >>
>> >> >> > >> A new standard fault, e.g. completionConditionFailure,
>> >> should be
>> >> >> > >> introduced to notify that the completion condition of a
>> >> >> > flow activity
>> >> >> > >> evaluated to false (note: all concurrent activities
>> have been
>> >> >> > >> completed). The fault is thrown in the scope enclosing the
>> >> >> > flow element.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Completion condition and links
>> >> >> > >>
>> >> >> > >> ==============================
>> >> >> > >>
>> >> >> > >> There should be no difference between a flow activity
>> with a
>> >> >> > >> completion condition and a flow activity without
>> >> >> > completion condition.
>> >> >> > >> For example, if the completion condition fails all links
>> >> >> > leaving the
>> >> >> > >> flow activity should have value "false" (or be reverted to
>> >> >> > a negative
>> >> >> > >> status).
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> There are just a few additional rules:
>> >> >> > >>
>> >> >> > >> (1) Let's assume enclosed activity A is the source of a
>> >> >> > link. If the
>> >> >> > >> completion condition evaluates to true and activity A is
>> >> >> > not completed
>> >> >> > >> it will be terminated and the value of the link will be
>> >> >> > set to "false".
>> >> >> > >>
>> >> >> > >> (2) Let's assume enclosed activity A is the source of a
>> >> >> > link and the
>> >> >> > >> activity failed but the fault is "ignored" by the
>> enclosing
>> >> flow
>> >> >> > >> activity. The value of the link will be set to "false".
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> New function for completion condition of flavor "the
>> two most
>> >> >> > >> important requests completed"
>> >> >> > >>
>> >> >> > >>
>> >> >> >
>> ==============================================================
>> >> >> > ==============================
>> >> >> > >>
>> >> >> > >>
>> >> >> > >> For completion conditions of flavor "the two most
>> >> >> > important requests
>> >> >> > >> completed" standard attribute "name" must be specified
>> for all
>> >> >> > >> enclosing activities in order to be able to distinguish
>> >> them. In
>> >> >> > >> addition a new function, e.g. isCompleted('activityName')
>> >> must be
>> >> >> > >> introduced. The semantics of the function is: if activity
>> >> >> > completed
>> >> >> > >> successfully the function returns value true.
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Example
>> >> >> > >>
>> >> >> > >> <completionCondition expression=
>> >> >> > >>
>> >> >> > >> "isCompleted('A') AND
>> isCompleted('B')" >> > >>
>> >> >> > >> </completionConditions>
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> > >>
>> >> >> > >> Regards,
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> Ivana
>> >> >> > >>
>> >> >> > >> > >>
>> >> >> > >> -----Original Message-----
>> >> >> > >> *From:* Alex Yiu [mailto:alex.yiu@oracle.com]
>> >> >> > >> *Sent:* Samstag, 11. September 2004 00:49
>> >> >> > >> *To:* Axel Martens
>> >> >> > >> *Cc:* 'edwink@collaxa.com
>> >> >> > <mailto:edwink@collaxa.com>'; Trickovic,
>> >> >> > >> Ivana; 'satisht@microsoft.com
>> >> <mailto:satisht@microsoft.com>';
>> >> >> > >> 'wsbpel@lists.oasis-open.org
>> >> >> > >> <mailto:wsbpel@lists.oasis-open.org>'; Alex Yiu
>> >> >> > >> *Subject:* Re: [wsbpel] Issue 6 - Rough draft of
>> >> >> > proposal for vote
>> >> >> > >>
>> >> >> > >>
>> >> >> > >> Hi, Axel,
>> >> >> > >>
>> >> >> > >> Thanks for liking parts of my proposal so far.
>> >> >> > >> Actually, the idea of my proposal is borrowed from a
>> >> part of
>> >> >> > >> presentation from Ivana and Dieter Roller in March
>> F2F.
>> >> I just
>> >> >> > >> generalize it to apply to <flow> also.
>> >> >> > >>
>> >> >> > >> About using links or not:
>> >> >> > >> I don't have a huge opposition to Axel's proposal
>> >> >> > which enriches
>> >> >> > >> the semantics of joinCondition evaluation. However, it
>> >> >> > is not that
>> >> >> > >> difficult for people to make mistakes in
>> joinCondition.
>> >> >> Look at
>> >> >> > >> the 2-out-of-3 example. The join condition already
>> gets so
>> >> >> > >> complicated. If people make a mistake in their
>> >> >> > joinCondition, the
>> >> >> > >> whole flow can get struck for no good reasons. (The
>> >> >> > >> completeCondition approach will less likely to have
>> >> >> > the whole flow
>> >> >> > >> struck. Because, it does not introduce a new parallel
>> >> >> > activity in
>> >> >> > >> the flow). But, if this is what Petri-net-oriented and
>> >> >> > >> control-link-oriented audience really want, I can
>> >> >> > accept it in a
>> >> >> > >> sense, as long as this is not the only way to achieve
>> >> similar
>> >> >> > >> business logic.
>> >> >> > >>
>> >> >> > >> About static vs dynamic parallelism:
>> >> >> > >> Static parallelism is basically <flow> construct in
>> >> >> > BPEL. Dynamic
>> >> >> > >> parallelism is "parallel forEach" or "bundle". Issue 4
>> >> >> > and 147 are
>> >> >> > >> related issues.
>> >> >> > >> >
>> >> >>
>> http://www.choreology.com/external/WS_BPEL_issues_list.html#Issue4
>> >> >> > >> >
>> >> >>
>> http://www.choreology.com/external/WS_BPEL_issues_list.html#Issue147
>> >> >> > >>
>> >> >> > >> About "Terminating still running tasks versus
>> >> proceeding in
>> >> >> > >> control flow while those tasks are
>> >> >> > >> still running":
>> >> >> > >> I am not 100% that I understand your question. Let me
>> >> try to
>> >> >> > >> answer it anyway. The completeCondition is about
>> >> triggering
>> >> >> > >> termination of still-running tasks. The "proceeding in
>> >> control
>> >> >> > >> flow" (if I understand you correctly) will be handled
>> >> >> > by an outter
>> >> >> > >> flow. [I guess it is related to (hotel and (train or
>> >> >> > plane)) flow??]
>> >> >> > >>
>> >> >> > >> About changes of "forcedTermination" fault handler:
>> >> >> > >> If you got a chance to see some recent emails on Issue
>> >> >> > 135, Satish
>> >> >> > >> has recently suggested to remove the notion
>> >> >> "forcedTermination"
>> >> >> > >> fault and replace its fault handler with
>> cancelHandler.
>> >> Frank,
>> >> >> > >> Yaron, Edwin and I all agree with this direction.
>> Because,
>> >> >> > >> overloading fault with the concept of
>> >> "forcedTermination" is a
>> >> >> > >> "false economy" and it creates quite a bit of
>> >> >> > unnecessary confusion.
>> >> >> > >>
>> >> >> > >> I don't think we should go back to this route or even
>> >> further
>> >> >> > >> overload the "forcedTermination" fault handler
>> >> >> > semantics. Because,
>> >> >> > >> fault handling is way too generic and the changes you
>> >> >> mentioned
>> >> >> > >> will create even more confusion. (e.g. Will this
>> >> >> > change of marking
>> >> >> > >> as "completed" apply to all "forcedTermination" fault
>> >> >> handler /
>> >> >> > >> cancel handler of all scopes? )
>> >> >> > >>
>> >> >> > >> I guess most of us agree that we should have a new
>> >> >> mechanism to
>> >> >> > >> kill / do an early completion of a flow in a nice and
>> >> >> > clean way.
>> >> >> > >> However, overloading a standard fault handler does not
>> >> >> > seem to be
>> >> >> > >> the best one. I would rather introduce a construct
>> >> >> > which is very
>> >> >> > >> specific to <flow> or parallel-forEach. For
>> example, this
>> >> >> > >> <completeCondition> construct or maybe a new activity
>> >> called
>> >> >> > >> <completeFlow />. I will send out more emails on
>> >> >> > joint thinking
>> >> >> > >> of both Issue 6 and Issue 135. Please stay tuned.
>> >> >> > >>
>> >> >> > >>
>> >> >> > >> Thanks!
>> >> >> > >>
>> >> >> > >>
>> >> >> > >>
>> >> >> > >> Regards,
>> >> >> > >> Alex Yiu
>> >> >> > >>
>> >> >> > >>
>> >> >> > >> Axel Martens wrote:
>> >> >> > >>
>> >> >> > >>>
>> >> >> > >>> Hi,
>> >> >> > >>>
>> >> >> > >>> I like the simplicity of the syntax of Alex's
>> >> >> > proposal. Although,
>> >> >> > >>> for me it is quite easy to model in terms of links
>> and
>> >> join
>> >> >> > >>> conditions, and I want to keep my proposal alive
>> >> >> > (because of the
>> >> >> > >>> minimal changes to BPEL's syntax and semantics), it
>> >> >> > looks like a
>> >> >> > >>> nice macro to provide more convenience to the
>> customers.
>> >> >> > >>>
>> >> >> > >>> Alex, could you shortly explain to me, what do you
>> >> >> > mean by static
>> >> >> > >>> and dynamic parallelism? How do you handle the two
>> >> >> > different cases
>> >> >> > >>> after evaluating the completeCondition: Terminating
>> >> >> > still running
>> >> >> > >>> tasks versus proceeding in control flow while those
>> >> tasks are
>> >> >> > >>> still running (Sorry, I missed your previous emails)?
>> >> >> > >>>
>> >> >> > >>> I agree to Alex's opinion, that we need a
>> mechanism to
>> >> kill
>> >> >> > >>> parallel flow nice and clean. This could be done
>> >> >> > either by a new
>> >> >> > >>> mechanism which does not throw a fault or by changing
>> >> the way
>> >> >> > >>> fault are handled. I have discussed already an
>> example
>> >> of the
>> >> >> > >>> second case with Ivana, and I like to tell you,
>> what I
>> >> >> have in
>> >> >> > >>> mind. Look at the following example:
>> >> >> > >>>
>> >> >> > >>> <scope name="scopeFlow">
>> >> >> > >>> ...
>> >> >> > >>> <flow>
>> >> >> > >>> <link name="linkA"/>
>> >> >> > >>> <link name="linkB"/>
>> >> >> > >>>
>> >> >> > >>> <scope name="scopeA">
>> >> >> > >>> ...
>> >> >> > >>> <invoke name="A" ...>
>> >> >> > >>> <source linkName="linkA" ...>
>> >> >> > >>> </invoke>
>> >> >> > >>> </scope>
>> >> >> > >>>
>> >> >> > >>> <scope name="scopeB">
>> >> >> > >>> ...
>> >> >> > >>> <invoke name="B" ...>
>> >> >> > >>> <source linkName="linkB" ...>
>> >> >> > >>> </invoke>
>> >> >> > >>> </scope>
>> >> >> > >>>
>> >> >> > >>> <throw name="C" faultName="bpws:forcedCompletion"
>> >> >> > >>> joinCondition="linkA OR linkB"
>> >> >> > >>> joinEvaluation="immediate">
>> >> >> > >>> <target linkName="linkA" ...>
>> >> >> > >>> <target linkName="linkB" ...>
>> >> >> > >>> </throw>
>> >> >> > >>>
>> >> >> > >>> </flow>
>> >> >> > >>> </scope>
>> >> >> > >>>
>> >> >> > >>> First, I explain the situation: In the example above,
>> >> >> > activity C
>> >> >> > >>> will be executed if one of the two activities A
>> and B was
>> >> >> > >>> successfully completed. Activity C throws the fault
>> >> >> > >>> "forcedCompletion". Like each other fault, this
>> >> >> > forces the scope
>> >> >> > >>> "scopeFlow" to terminate still running activities.
>> >> >> > Assume, there
>> >> >> > >>> was a fault handler defined in this scope which
>> >> >> > catches the fault
>> >> >> > >>> "forcedCompletion" (omitted in here), the process
>> >> >> > continues after
>> >> >> > >>> scope "scopeFlow". A problem arises, if scope
>> >> >> > "scopeFlow" should
>> >> >> > >>> be compensated. Because it was exited from a fault
>> >> >> handler, no
>> >> >> > >>> compensation handler was installed.
>> >> >> > >>>
>> >> >> > >>> Now, I explain my solution: In the example, I have
>> >> >> > chosen a new
>> >> >> > >>> "standard" fault name: "forcedCompletion". The only
>> >> necessary
>> >> >> > >>> change is to allow a fault handler that catches this
>> >> fault to
>> >> >> > >>> install a compensation handler for the same scope,
>> >> >> > i.e. to mark
>> >> >> > >>> the scope "scopeFlow" as "completed" instead of
>> "exited".
>> >> >> > >>>
>> >> >> > >>> The standard compensation mechanism will only undo
>> those
>> >> >> > >>> ("scoped") activities within the scope, which
>> >> >> > actually have been
>> >> >> > >>> successfully completed, i.e. scopeA or scopeB or may
>> >> be both.
>> >> >> > >>>
>> >> >> > >>> Axel.
>> >> >> > >>> ----------------------------------------
>> >> >> > >>> Axel Martens
>> >> >> > >>>
>> >> >> > >>> Post Doc Researcher
>> >> >> > >>> Component Systems Group
>> >> >> > >>> IBM TJ Watson Research Center
>> >> >> > >>> Hawthorne, NY (USA)
>> >> >> > >>> Phone: (914) 784-7480
>> >> >> > >>> E-mail: amarten@us.ibm.com
>> <mailto:amarten@us.ibm.com>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> *Alex Yiu <alex.yiu@oracle.com>
>> >> <mailto:alex.yiu@oracle.com>*
>> >> >> > >>>
>> >> >> > >>> 09/10/2004 12:10 AM
>> >> >> > >>>
>> >> >> > >>> > >>> To
>> >> >> > >>> Alex Yiu <alex.yiu@oracle.com>
>> >> >> > <mailto:alex.yiu@oracle.com>
>> >> >> > >>> cc
>> >> >> > >>> "Trickovic, Ivana" <ivana.trickovic@sap.com>
>> >> >> > >>> <mailto:ivana.trickovic@sap.com>, Axel
>> >> >> > Martens/Watson/IBM@IBMUS,
>> >> >> > >>> "'edwink@collaxa.com'"
>> <mailto:%27edwink@collaxa.com%27>
>> >> >> > >>> <edwink@collaxa.com> <mailto:edwink@collaxa.com>,
>> >> >> > >>> "'satisht@microsoft.com'"
>> >> >> <mailto:%27satisht@microsoft.com%27>
>> >> >> > >>> <satisht@microsoft.com>
>> <mailto:satisht@microsoft.com>,
>> >> >> > >>> "'wsbpel@lists.oasis-open.org'"
>> >> >> > >>> <mailto:%27wsbpel@lists.oasis-open.org%27>
>> >> >> > >>> <wsbpel@lists.oasis-open.org>
>> >> >> > >>> <mailto:wsbpel@lists.oasis-open.org>, Alex Yiu
>> >> >> > >>> <alex.yiu@oracle.com> <mailto:alex.yiu@oracle.com>
>> >> >> > >>> Subject
>> >> >> > >>> Re: [wsbpel] Issue 6 - Rough draft of proposal
>> >> for vote
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> Hi,
>> >> >> > >>>
>> >> >> > >>> Here are some examples how to use
>> completeCondition to
>> >> >> express
>> >> >> > >>> similar business logic in Axel's previous email:
>> >> >> > >>>
>> >> >> > >>> (A) "Select one out of three" example:
>> >> >> > >>> <flow>
>> >> >> > >>> <completeCondition *branch="1"* />
>> >> >> > >>> <invoke name="CheckAirlineA" ... />
>> >> >> > >>> <invoke name="CheckAirlineB" ... />
>> >> >> > >>> <invoke name="CheckAirlineC" ... />
>> >> >> > >>> </flow>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> (B) "Select two out of three" example:
>> >> >> > >>> <flow>
>> >> >> > >>> <completeCondition *branch="2"* />
>> >> >> > >>> <invoke name="AskRefereeA" ... />
>> >> >> > >>> <invoke name="AskRefereeB" ... />
>> >> >> > >>> <invoke name="AskRefereeC" ... />
>> >> >> > >>> </flow>
>> >> >> > >>>
>> >> >> > >>> As you guys can see, the completeCondition
>> declaration is
>> >> >> very
>> >> >> > >>> straight forward and simple. No complicated links and
>> >> >> > >>> joinCondition usage.
>> >> >> > >>>
>> >> >> > >>> (C) "(Plane or Train) and Hotel" example: It would
>> >> become two
>> >> >> > >>> flow constructed (nested).
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> <assign> ... <to variable="planeResult"></assign>
>> >> >> > >>> <!-- initialize "planeResult" with NOT-OK value -->
>> >> >> > >>> <assign> ... <to variable="trainResult"></assign>
>> >> >> > >>> <!-- initialize "trainResult" with NOT-OK value
>> --> *
>> >> >> > >>> <flow name="checkIterinary">*
>> >> >> > >>> *<flow name="PlaneOrPlane">*
>> >> >> > >>> <completeCondition>
>> >> >> > >>> fn:planeOK(planeResult) *or*
>> >> >> > fn:trainOK(trainResult)
>> >> >> > >>> </completeCondition>
>> >> >> > >>> <invoke name="CheckPlane"
>> >> >> > outputVariable="planeResult" ... />
>> >> >> > >>> <invoke name="CheckTrain"
>> >> >> > outputVariable="trainResult" ... />
>> >> >> > >>> *</flow> *
>> >> >> > >>> <invoke name="checkHotel" /> *
>> >> >> > >>> </flow>
>> >> >> > >>> <switch name="bookingSwitch">*
>> >> >> > >>> <case>
>> >> >> > >>> <condition>
>> >> >> > >>> (fn:planeOK(planeResult) *or*
>> >> fn:trainOK(trainResult))
>> >> >> > >>> *and* fn:hotelOK(hotelResult)
>> >> >> > >>> </condition>
>> >> >> > >>> <invoke name="invokeBooking" ... />
>> >> >> > >>> </case>
>> >> >> > >>> <otherwise>
>> >> >> > >>> <invoke name="writeInformation" ... />
>> >> >> > >>> </otherwise> *
>> >> >> > >>> </switch>*
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> Please note that regardless whether we pick a
>> >> link-oriented
>> >> >> > >>> approach or completeCondition approach:
>> >> >> > >>>
>> >> >> > >>> * The initialization of result variables are
>> >> >> > needed because
>> >> >> > >>> of potential cancellation of one of the invoke
>> >> between
>> >> >> > >>> train and plane
>> >> >> > >>> * The "fn:*()" represents the logic to determine
>> >> >> whether a
>> >> >> > >>> traveling resource is available. They are
>> used in
>> >> >> either
>> >> >> > >>> the transitionCondition of links or the
>> >> condition of
>> >> >> > >>> switch/case.
>> >> >> > >>>
>> >> >> > >>> As you guys see, we don't need declare to six
>> links. The
>> >> >> > >>> completeCondition and case-condition are much simpler
>> >> >> > and easier
>> >> >> > >>> to understand.
>> >> >> > >>>
>> >> >> > >>> I attach a diagram to illustrate the above flows.
>> >> >> > >>>
>> >> >> > >>> I guess we can still more time in terms of
>> refiniment of
>> >> >> > >>> joinCondition evaluation. However, I don't think that
>> >> >> > should be
>> >> >> > >>> the only approach to achieve complete condition
>> related
>> >> >> logic.
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> Thanks!!!
>> >> >> > >>>
>> >> >> > >>> Regards,
>> >> >> > >>> Alex Yiu
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> Alex Yiu wrote:
>> >> >> > >>>
>> >> >> > >>> Hi,
>> >> >> > >>>
>> >> >> > >>> +1 to what Ivana said in general.
>> >> >> > >>>
>> >> >> > >>> Few points to add:
>> >> >> > >>>
>> >> >> > >>> * Axel's proposed enhancement to control links
>> >> evaluation
>> >> >> > >>> works to an extent for static parallelism >
>> (e.g.
>> >> >> <flow>).
>> >> >> > >>> However, control links do not work well in
>> dynamic
>> >> >> > >>> parallelism (e.g. "parallel forEach" or
>> >> >> > "bundle"). I think
>> >> >> > >>> the notion of completeCondition (borrowed from
>> >> Ivana
>> >> >> and
>> >> >> > >>> DK) is general enough and it should be applied
>> >> to both
>> >> >> > >>> static and dynamic parallelism. A general
>> >> >> > completeCondition
>> >> >> > >>> mechanism will be easier for BPEL users to
>> learn.
>> >> >> > >>> * Even in a pure static parallelism case,
>> >> >> > completeCondition
>> >> >> > >>> has much better code clarity. It is more
>> >> declarative
>> >> >> and
>> >> >> > >>> easier for BPEL users to understand. It will
>> >> eliminate
>> >> >> > >>> significant amount of joinCondition
>> >> >> > programming, which may
>> >> >> > >>> be error prone. (I will send another email
>> later to
>> >> >> show
>> >> >> > >>> how completeCondition can be used to express
>> the
>> >> same
>> >> >> > >>> semantics of Axel's example).
>> >> >> > >>> * In one of my previous emails, I also tried to
>> >> >> > use a "macro"
>> >> >> > >>> way to illustrate how outstanding running flows
>> >> can be
>> >> >> > >>> cancelled by throwing a fault within a
>> scope. The
>> >> >> > >>> illustration has the same compensation handler
>> >> >> > installation
>> >> >> > >>> problem that Ivana has pointed out. The
>> >> "illustraction
>> >> >> > >>> macro" does NOT carry a desirable and intended
>> >> >> > semantics.
>> >> >> > >>> We need to create / describe a new mechanism to
>> >> cancel
>> >> >> > >>> parallel flow without throwing a fault. (That
>> >> >> > was discussed
>> >> >> > >>> briefly between Edwin and me at Oracle).
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> Thanks!
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> Regards,
>> >> >> > >>> Alex Yiu
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>>
>> >> >> > >>> Trickovic, Ivana wrote:
>> >> >> > >>> Axel,
>> >> >> > >>> > >>> I find the idea interesting. In fact, I
>> was
>> >> >> discussing the
>> >> >> > >>> completion condition issue with Dieter Koenig during
>> >> >> > the last f2f
>> >> >> > >>> meeting and his suggestion was also to try to resolve
>> >> >> > this issue
>> >> >> > >>> using links. And we identified that several
>> changes need
>> >> >> to be
>> >> >> > >>> done, including removing restriction for
>> >> >> > jonCondition, that "the
>> >> >> > >>> join condition is evaluated as soon as all incoming
>> >> >> > links of the
>> >> >> > >>> activity are determined" - so definitely "immediate"
>> >> >> semantics
>> >> >> > >>> needs to be introduced.
>> >> >> > >>> > >>> I have the following comments on your
>> >> proposal.
>> >> >> > >>> 1. In your proposal you are using a fault
>> >> >> > >>> (bpws:forcedTermination) to terminate all active
>> parallel
>> >> >> > >>> branches. But this changes the outcome of the flow
>> >> >> > activity. It
>> >> >> > >>> will always end abnormally and compensation handler
>> >> (if it is
>> >> >> > >>> defined) will never be installed. Although completion
>> >> >> > condition
>> >> >> > >>> has evaluated to true and needed activities have
>> >> completed
>> >> >> the
>> >> >> > >>> enclosing flow activity will end abnormally. Is this
>> >> really
>> >> >> > >>> intended semantics?
>> >> >> > >>> > >>> 2. Your proposal does not address some
>> pain
>> >> >> points.
>> >> >> > For example,
>> >> >> > >>> in case of "N out of M", N<M there many possible
>> >> >> "variations":
>> >> >> > >>> (A) One enclosed activity may experience problems but
>> >> >> > the <flow>
>> >> >> > >>> activity may succeed
>> >> >> > >>> (B) One of enclosed activities may experience a
>> severe
>> >> error,
>> >> >> > >>> which may have impact on the <flow> activity
>> >> >> > >>> The question is what to do with running activities?
>> >> >> > In the latter
>> >> >> > >>> case, reasonable behavior would be: if one enclosed
>> >> >> > activity does
>> >> >> > >>> not succeed other running activities should be
>> >> >> > cancelled and the
>> >> >> > >>> flow activity should try to recover. In the former
>> >> case, we
>> >> >> > >>> should allow active parallel activities to complete
>> >> >> > their work.
>> >> >> > >>> This is not supported in your proposal.
>> >> >> > >>> > >>> Regards,
>> >> >> > >>> > >>>
>> >> >> > >>> Ivana
>> >> >> > >>>
>> >> >> > >> [stuff deleted]
>> >> >> > >>
>> >> >> > >
>> >> >> >
>> >> >> > To unsubscribe from this mailing list (and be removed from
>> >> >> > the roster of the OASIS TC), go to
>> >> >> >
>> http://www.oasis-open.org/apps/org/workgroup/wsbpel/members/le
>> >> >> > ave_workgroup.php.
>> >> >> >
>> >> >>
>> >> >> To unsubscribe from this mailing list (and be removed from the
>> >> roster
>> >> >> of the OASIS TC), go to
>> >> >>
>> >>
>> http://www.oasis-open.org/apps/org/workgroup/wsbpel/members/leave_workgroup.php.
>>
>> >>
>> >> >>
>> >> >>
>> >> >
>> >> > To unsubscribe from this mailing list (and be removed from the
>> roster
>> >> > of the OASIS TC), go to
>> >> >
>> >>
>> http://www.oasis-open.org/apps/org/workgroup/wsbpel/members/leave_workgroup.php.
>>
>> >>
>> >> >
>> >> >
>> >> >
>> >>
>> >> To unsubscribe from this mailing list (and be removed from the
>> roster
>> >> of the OASIS TC), go to
>> >>
>> http://www.oasis-open.org/apps/org/workgroup/wsbpel/members/leave_workgroup.php.
>>
>> >>
>> >>
>> >
>>
>> To unsubscribe from this mailing list (and be removed from the roster
>> of the OASIS TC), go to
>> http://www.oasis-open.org/apps/org/workgroup/wsbpel/members/leave_workgroup.php.
>>
>>
>
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