W3C home > Mailing lists > Public > public-ws-chor@w3.org > September 2003

The requirements on message 'correllation'

From: Fletcher, Tony <Tony.Fletcher@choreology.com>
Date: Wed, 3 Sep 2003 10:02:41 +0100
Message-ID: <221369570DEDF346AE42821041345E89264B76@exchange1.corp.choreology.com>
To: <public-ws-chor@w3.org>
Dear Colleagues,
I would like to restate what I was trying to say yesterday on the
teleconference to make sure I expressed myself clearly.
I agree very much with Yaron that we should try to winkle out the basics
from our discussions.
For me three basics arising from this discussion are:
1)  Each message received by a system needs to have information
associated with it somehow that is sufficient to unambiguously
implicitly or explicitly identify its target programme (/instance /
2)  It should be an option for messages to carry information in some
manner that unambiguously identifies the type and instance of that type
of a choreography description that it is a part of.
3)  If a choreography type and instance of that type is being followed
then it should (must?) be possible to say that the message is part of
the instance and either is consistent with its normal operation or
indicates that an error has occurred in following the choreography.
I suspect we all agree with 1) and take it as a given.
I suspect we probably all (or a majority) agree with 3) although it may
have some implications (requirements) on the Choreography language.
I suspect the one in dispute is 2)
If the systems are directly implementing and at least in some direct
sense 'executing' the choreography instance then it seems to me very
reasonable that the messages should carry an explicit identifier for the
choreography type and instance they relate to that is recognised at the
target system.
But picking up an argument that I think it was Frank made, it may often
be the case that the systems are not programmatically aware that they
are following a choreography instance.  Suppose that a description of
choreography is agreed amongst some cooperating parties using our CDL.
Each party then implements using BPEL as an intermediate step (or
directly using a programming language).  When this choreography is
followed the systems are in fact following an unfolding instance of the
choreography, but they are also following an unfolding instance of
interacting BPEL instances (or programme instances) and it is these that
the messages will need to directly identify and target. 

Best Regards,



Tony Fletcher

Technical Advisor 
Choreology Ltd.
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Received on Wednesday, 3 September 2003 05:03:15 UTC

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