Vinky,
"Did not complete" means that the activity did not complete successfully
and there was no fault handler that could handle the fault without rethrowing
it.
In case of scopes, we have the following
outcomes:
(1) Scope completes
successfully
(2) A fault has been thrown within the scope and
there is a fault handler local to that scope which can handle the fault without
rethrowing it; in this case the process will continue with normal processing in
the enclosing scope
(3) A fault has been thrown within the scope and no
fault handler can perform clean up - so the fault may be rethrown or different
one may be thrown; in this case the process will terminate processing in the
enclosing scope
I hope this explanation helps.
Regards,
Ivana
-----Original Message-----
From:
[mailto:]
Sent: Montag, 13. September
2004 02:13
To: Trickovic, Ivana; ;
Cc: ; ;
; ; ;
Subject: RE: [wsbpel] Issue 6 - Rough
draft of proposal for vote
Hello Ivana,
Could you please clarify the following paragraph:
"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."
In
this paragraph when you say "did not complete", do you mean
"did not complete successfully". I am assuming the
faults will be generated ONLY by activities that are actually completed and
not by activities still in RUNNING state?
As
I understand a BPEL process engine would only evaluate the
<completeCondition> for a process instance everytime an activity within
in the <flow> completes (SUCCESSFULLY or with a FAULT).
thanks,
-Vinky
-----Original Message-----
From: Trickovic, Ivana
[mailto:]
Sent: Saturday, September 11,
2004 5:10 PM
To: Alex Yiu; Axel Martens
Cc: Frank
Leymann; Dieter Roller; Dieter Koenig1; '';
''; ''
Subject:
RE: [wsbpel] Issue 6 - Rough draft of proposal for vote
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:]
Sent: Samstag, 11. September 2004
00:49
To: Axel Martens
Cc: '';
Trickovic, Ivana; ''; '';
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:
Alex Yiu <>
09/10/2004 12:10 AM
To
Alex Yiu <>
cc
"Trickovic,
Ivana" <>,
Axel Martens/Watson/IBM@IBMUS, "''"
<>,
"''"
<>,
"''"
<>,
Alex Yiu <>
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]
