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Re: "Message" semantics and composition -- WAS Grounding Choreographies (the atoms)

From: Assaf Arkin <arkin@intalio.com>
Date: Mon, 21 Jul 2003 12:57:36 -0700
Message-ID: <3F1C45B0.50107@intalio.com>
To: Andrew Berry <andyb@whyanbeel.net>
CC: Francis McCabe <fgm@fla.fujitsu.com>, public-ws-chor@w3.org

Andrew Berry wrote:

>
> This approach has many advantages.  In particular, when speaking of a 
> set of autonomous participants in a choreography, the behaviour of 
> each participant will be based entirely on what they are able to 
> observe from their locality.  This protects their interests and 
> ensures their autonomy.  The choreography should respect their 
> autonomy and explicitly specify the behaviour of participants based on 
> what they are able to observe locally.  The causal relationships 
> defined by the choreography then specify the expectations of other 
> participants resulting from local behaviour of a participant.

+1

> Explicitly separating the local behaviour from causal relationships 
> also has considerable advantages for composition.  Consider Arkin's 
> example in 
> http://lists.w3.org/Archives/Public/public-ws-chor/2003Jul/0134.html: 
> we want to re-use the "message" interaction in many choreographies.  
> If a message is specified from a senders perspective as a send 
> followed by an acknowledgement, we can use this sender behaviour in a 
> number of different scenarios, including a simple message, a delegated 
> message or even a multicast message (e.g. for high availability).  If 
> we "bind" the sender's message semantics to a particular interaction 
> model then we significantly reduce the possible compositions of this 
> behaviour.

I am less in agreement on this point. While I perfectly understand the 
premise and agree with it from one specific perspective, it is not clear 
why there would be a constrast since causality can both occur inside a 
locality, and can depend on things that may be true regardless of 
autonomy or locality.

For example, if we know that a service receives X and replies with Y, as 
a requestor of that service, without violating my autonomy and 
regardless of my location, if I send X I expect to receive Y. I am fully 
autonomous in every respect, and my locality can change, but that 
causality is something I expect to happen, hence define an interaction 
around it.

arkin


>
> Ciao,
>
> AndyB
>
>>
>> Frank
>>


-- 
"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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Received on Monday, 21 July 2003 15:59:00 GMT

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