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Grounding Choreographies (the atoms) - WAS Simple Choreography composition suggestion

From: Steve Ross-Talbot <steve@enigmatec.net>
Date: Thu, 17 Jul 2003 10:13:42 +0100
Cc: public-ws-chor@w3.org
To: "Champion, Mike" <Mike.Champion@SoftwareAG-USA.com>
Message-Id: <F5F0F59D-B836-11D7-931D-000393AD2AA6@enigmatec.net>

   At the considerable risk of adding further confusion to the 
discussion I would like to attempt to clarify what I said on the call 
with respect to the grounding of a choroegraphy.


   Here is how I see it:

   A "web service" choreography, as distinct from any other 
choreography, is grounded to a minimum of two web services instances. 
This may mean that the web services are the same web services but 
different instance or it may mean that they are distinct (personally I 
have a hard time seeing what they would be anything other than the 
latter) such that I can observe a communication between them.

   A communication is a minimum of a single message sent from one web 
service to another web service.

   It may be the case that in receiving or indeed sending a message the 
sending web service and/or the receiving web service can be externally 
observed to change their behaviour.

   A "web service" choreography, as distinct from any other 
choreography, is based on externally observable behaviour where this 
behaviour is defined in terms of communications between web services 
and externally observed behavioral changes of a web service.

   For the avoidance of doubt, a Message Exchange Pattern (MEP) or any 
mechanism that describes communication between two parties can be said 
to be a choreography. But it cannot be said to be a "web service" 
choreography.


Cheers

Steve T


On Wednesday, July 16, 2003, at 02:57  pm, Champion, Mike wrote:

>
>
>
>> -----Original Message-----
>> From: Fletcher, Tony [mailto:Tony.Fletcher@choreology.com]
>> Sent: Wednesday, July 16, 2003 9:12 AM
>> To: public-ws-chor@w3.org
>> Subject: FW: Simple Choreography composition suggestion
>>
>
>>
>> The point I disagree with is the notion that something is not a
>> Choreography if somewhere, at some level it involves 'orchestration'
>> within a single system.  If we accept this notion /
>> restriction it means
>> that you can only have Choreographies involving exactly two parties
>> where each party only plays a single role - we will not be
>> able to have
>> Choreographies with more than two parties / roles at all.
>
> That wasn't my intent, FWIW.  All sorts of compositions and 
> decompositions
> can occur within a "choreography," but IMHO only those that involve the
> globally visible shared state are in scope for the choreography 
> description
> language we are developing.  The discussion yesterday got me 
> re-thinking all
> sorts of things ... if the fundamental unit of a "choreography" is a 
> Web
> service invocation / MEP, then all sorts of implementation details of 
> the
> service that involved "orchestrated" interactions behind the scenes are
> abstracted away, but if the fundamental unit is a message, then all 
> those
> messages behind the scenes have to be accounted for somehow.  I'm as
> confused as anyone at this point.
>
> By all means let's make sure that we don't box ourselves into a corner 
> based
> on some preliminary guesses about what terms mean!
>
>
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Received on Thursday, 17 July 2003 05:13:57 GMT

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