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

From: Fletcher, Tony <Tony.Fletcher@choreology.com>
Date: Wed, 23 Jul 2003 10:45:11 +0100
Message-ID: <221369570DEDF346AE42821041345E891957A7@exchange1.corp.choreology.com>
To: <public-ws-chor@w3.org>

Dear Colleagues,

I am a bit behind with mail, so someone may have already made this
point, but I would like to suggest that we need (at least) two terms not
just one (agent).  Some other groups have used 'party' and 'role' where
a party is a single administrative domain (at least - I am sure has
other characteristics as well) and can play several roles
(simultaneously, overlapped or sequentially or any combination).  There
can by 'internal' communication between the roles a party plays but all
communications between the roles that different parties play is via
external communications (messages / interactions of direct interest to
the Choreography).

Thus if we do not use these two terms I think we need two which are
their 'moral equivalent'.

Best Regards     Tony
A M Fletcher
 
Cohesions  (TM)
 
Business transaction management software for application coordination
www.choreology.com
 
Choreology Ltd., From 4 August: 68 Lombard Street, London EC3N 9LJ
UK
Tel: +44 (0) 8707 390076   Fax: +44 (0) 8707 390077  Mobile: +44 (0)
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-----Original Message-----
From: public-ws-chor-request@w3.org
[mailto:public-ws-chor-request@w3.org] On Behalf Of Assaf Arkin
Sent: 17 July 2003 19:32
To: Francis McCabe
Cc: Martin Chapman; Steve Ross-Talbot; Champion, Mike;
public-ws-chor@w3.org
Subject: Re: Grounding Choreographies (the atoms) - WAS Simple
Choreography composition suggestion



So a Web Service Choreography does not choreograph Web services, it 
choreographs agents?

arkin

Francis McCabe wrote:

>
> +1.
>
> Following the form of the WSA, we have agents that provide and request

> Web services. This is based on the intuition that a service is 
> fundamentally about the potential for action, and that actors 
> (computational and otherwise) are the entities that do the acting.
>
> Frank
>
> On Thursday, July 17, 2003, at 09:16  AM, Martin Chapman wrote:
>
>>
>> I think there is a fundamental terminology issue here that needs to
>> be cleared up. An entity (avoiding any overloaded word) that sends a 
>> message to a web service (and may expect a response depending on the 
>> wsdl) doesn not iteslf
>> have to be a web service. This is the most fundamental building
block.
>> Furthermore this interaction supports an MEP (in soap teminology) and
>> pattern (in wsd teminology).
>> Perosnllay if we can not describe these meps in a choreography 
>> language we
>> have failed, and hence I do not think that mep choreogaprhy is any 
>> different
>> from web service choreography.
>>
>> Martin.
>>
>>
>>
>>> -----Original Message-----
>>> From: public-ws-chor-request@w3.org
>>> [mailto:public-ws-chor-request@w3.org]On Behalf Of Steve Ross-Talbot
>>> Sent: Thursday, July 17, 2003 2:14 AM
>>> To: Champion, Mike
>>> Cc: public-ws-chor@w3.org
>>> Subject: Grounding Choreographies (the atoms) - WAS Simple 
>>> Choreography composition suggestion
>>>
>>>
>>>
>>>    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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>>>
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>>


-- 
"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 Wednesday, 23 July 2003 05:45:24 GMT

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