RE: [wsbpel] Link semantics and control dependencies

["Satish Thatte" <satisht@microsoft.com>]

I think we explicitly ban that in banning control cycles made with links.  Let me know if anyone thinks that is not clearly stated.

________________________________

From: Assaf Arkin [mailto:arkin@intalio.com]
Sent: Mon 4/4/2005 11:56 PM
To: Satish Thatte
Cc: Dumas, Marlon; wsbpel@lists.oasis-open.org
Subject: Re: [wsbpel] Link semantics and control dependencies



the only other one I can think of is when the link order contradicts the
order of execution, e.g. if the first activity in a sequence is the
target, and the second activity is the source.

assaf

Satish Thatte wrote:

>Is there a case other than a link targeting an activity sourced at a
>parent activity in the nesting structure?  IOW is this an example or the
>only case?
>
>-----Original Message-----
>From: Assaf Arkin [mailto:arkin@intalio.com]
>Sent: Monday, April 04, 2005 7:40 PM
>To: Satish Thatte
>Cc: Dumas, Marlon; wsbpel@lists.oasis-open.org
>Subject: Re: [wsbpel] Link semantics and control dependencies
>
>Since A3 is allowed to begin (when selected) before A1 completes (in
>fact, A1 must complete after A3), a link dependency cannot be etablished
>
>between A1 and A3, so the link is invalid. Perhaps, we should be more
>clear about this in the spec, though I believe it says something about
>links not being valid when they contradict ordering of activities (e.g.
>links that reverse order of sequence):
>
>It is illegal to declare a link if a control dependency cannot be
>established between the source activity and target activity, for
>example, if the target activity is nested within the source activity
>(and vice versa), and therefore must complete before the source activity
>
>has completed.
>
>Assaf
>
>Satish Thatte wrote:
>
> 
>
>>Marlon,
>>
>>I am trying to fathom the link from A1 to A3.  Do you mean that A1 is
>>the switch activity and A3 is a nested case within the switch and there
>>is a link from A1 to A3?  If so then this is pathological.  I realize
>>that we probably don't ban it today explicitly but there is no way to
>>have A3 execute in this case, regardless of the A4 conundrum.
>>
>>Satish
>>
>>-----Original Message-----
>>From: Dumas, Marlon [mailto:marlon.dumas@sap.com]
>>Sent: Thursday, March 31, 2005 1:30 AM
>>To: wsbpel@lists.oasis-open.org
>>Subject: [wsbpel] Link semantics and control dependencies
>>
>>Hi,
>>
>>I believe that the following two fragments of the spec. contradict each
>>other and I would like to gather second opinions about it:
>>
>>In Section 12.5.1 (Link Semantics)
>>"If, during the performance of structured activity S, the semantics of
>>S dictate that activity X nested within S will not be performed as
>>part of the behavior of S, then the status of all outgoing links from
>>X is set to negative. An example is an activity within a branch that
>>is not taken in a switch activity..."
>>
>>In Section 13.4.2 (Default Compensation Order):
>>"If an activity A must complete before activity B begins, as a result
>>of the existence of a control path from A to B in the process
>>definition, then we say that B has a control dependency on A. Note
>>that control dependencies may occur due to control links in a <flow>
>>as well as due to constructs like <sequence>."
>>
>>To illustrate this contradiction, consider the following example:
>>
>><flow name="F">
>>link x1 goes from A1 to A3
>>link x2 goes from A3 to A4
>>
>>A1
>><switch name="Sw">
>>  case C1: A2
>>  case C2: A3
>></switch>
>>A4 [joinCondition = "not x2"]
>>
>></flow>
>>
>>Let's now consider the following execution: Flow F starts, and thus
>>action A1 and switch "Sw" are executed. Note that at this point A4 is
>>ready to start but does not start because its incoming link x2 has not
>>yet been determined. Let's now assume that condition C1 evaluates to
>>true and thus the corresponding branch is taken which results in
>>activity A2 being executed. According to the first quote from the
>>spec. above, the status of link x2 is then set to negative since
>>branch A3 was not taken. The joinCondition at A4 ("not x2") then
>>evaluates to True, and this results in A4 being executed. Note that at
>>this point in time, A1 has not yet completed.
>>
>>This seems to contradict the second quote above. Indeed, there is a
>>control path from A1 to A4 (i.e. a control link from A1 to A3 and
>>another one from A3 to A4), which means that A4 has a control
>>dependency on A1. Hence A4 cannot start before A1 has completed.
>>
>>Does anybody find any flaws in my reasoning?
>>
>>Thanks
>>
>>marlon
>>
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