Re: Issue - 52 - Issue Summary

[Assaf Arkin <arkin@intalio.com>]

Since I'm on mute all the time, it takes me before I can respond when my 
name is called.

Yaron, you quoted me correctly. I see the need for this capability, I 
would just prefer that we add a language feature to address is rather 
then rely on WSDL. This will allow us to better control the mechanism, 
and also allow tools to easily distinguish between intra-process and 
inter-process communication.

arkin

Yaron Goland wrote:

>Executive Summary:
>	Issue: How to enable intra-process communication (e.g. how to allow flows
>in the same process instance to share information).
>
>	Possible Solutions:
>
>		Shared Variables: General consensus that this is too hard to get right.
>
>		BPEL Messaging: Allow a BPEL process instance to send itself messages.
>There are concerns around deadlocks.
>
>		BPM Choice Points: An alternate programming language being developed in a
>separate OASIS TC, I have reviewed some material on it but do not feel that
>I understand it well enough to properly summarize it.
>
>		Other: Assaf and Satish have proposed not using BPEL messaging and agree
>to not liking shared variables but have not yet made an alternate proposal.
>
>Long Winded Version:
>
>Diane asked me to lead a conversation on issue 52 during Wednesday's phone
>call. I'm not sure if that is still on since she asked me to get out a
>summary by Monday and I was on vacation but just in case here is my summary
>of the threads on this subject to date.
>
>There seems to be consensus that currently there is no standardized
>mechanism other than shared variables to enable flows in the same process
>instance to communicate with each other (intra-process communication). There
>furthermore seems to be a consensus that if one wants to do intra-process
>communication then shared variables are a sub-optimal mechanism because they
>are very easy to get wrong.
>
>It was proposed that one could re-use the existing messaging facilities
>within BPEL to enable intra-process messaging as a solution to the problem
>of intra-process communication. In other words, we would enable flows in the
>same process instance to send each other messages using the normal BPEL
>messaging facilities.
>
>This led to a discussion of how to enable this scenario. Two solutions were
>offered.
>
>One solution was to use WSDL bindings to specify that a WSDL service was
>bound to the process instance. That way if the process should send that
>service a message then by definition the message must loop back to the same
>process instance. However there appeared to be consensus that there was no
>standard way to specify this at the WSDL level and no desire to introduce
>WSDL hacking.
>
>The alternate proposal was to introduce an attribute that could be used on
>role definitions to specify that both ends of the role point to the same
>process instance. This would allow the process to send messages to itself.
>For more details on this proposal and comparison of it to other proposals
>see http://lists.oasis-open.org/archives/wsbpel/200308/msg00158.html.
>
>Both Satish and Assaf didn't like the idea of using BPEL messaging for
>intra-process communication. Assaf was uncomfortable with the idea of
>defining WSDL interfaces strictly for intra-process use. Satish's objection
>was that using BPEL messaging for intra-process communication could lead to
>deadlocks within a single process instance. While deadlocks were always
>possible between BPEL processes Satish's contention is that the introduction
>of this feature would, for the first time, enable a deadlock within a single
>BPEL process instance. I need to follow up with Satish on this point since
>it is my understanding that it was always possible to cause deadlock within
>a BPEL process instance through shared variable access.
>
>Both Satish and Assaf want to use an alternate mechanism to the ones
>proposed but so far have made no concrete proposals for how to proceed.
>
>David Webber has suggested using BCM choice points. I reviewed the
>presentation he sent out and I must admit that I'm am still very unclear as
>to exactly what choice points do. It looked like some kind of rules based
>business language. I am also unclear as to how mature the choice point
>proposal is, what schedule it is on, how well its functionality meets BPEL's
>requirements, how interested BPEL and/or the choice point folks are on
>collaborating, etc. Hopefully David Webber will be available for the phone
>call and will be able to clarify issues around choice points.
>  
>


-- 
"Those who can, do; those who can't, make screenshots"

----------------------------------------------------------------------
Assaf Arkin                                          arkin@intalio.com
Intalio Inc.                                           www.intalio.com
The Business Process Management Company                 (650) 577 4700


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