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Re: Choreography awareness (was RE: Correlation Requirements)

From: Francis McCabe <fgm@fla.fujitsu.com>
Date: Mon, 8 Sep 2003 11:01:12 -0700
Cc: "'Burdett, David'" <david.burdett@commerceone.com>, <jdart@tibco.com>, "'Monica Martin'" <monica.martin@sun.com>, "'Yves Lafon'" <ylafon@w3.org>, "'Ugo Corda'" <UCorda@SeeBeyond.com>, "'Cummins Fred A'" <fred.cummins@eds.com>, <public-ws-chor@w3.org>
To: "Martin Chapman" <martin.chapman@oracle.com>
Message-Id: <6E8A8D78-E226-11D7-8B81-000393A3327C@fla.fujitsu.com>

Kind of.

Just as I fully expect most `end-point' Web services to be fairly 
simple, I expect most Web services will not themselves be choreography 
aware. It would be a failure on our part if we required a Web service 
to be choreography aware before it could participate. Remember, a key 
axiom in the WSA is that 'thou shalt not require knowledge of the 
implementation of the agent' in order to be able to use the service. 
The corollary of that is that the service may not be CDL-aware.

Similarly, I can see a role for CDLs as essentially documenting how to 
*use* services as much as *building* them. (As per your earlier 
comment, perhaps it is true that 'User agents' are more likely to be 
active consumers of a CDL than an end-point service.)

Frank

On Friday, September 5, 2003, at 05:02  PM, Martin Chapman wrote:

> I think itís a bit naÔve to think that an existing web service can 
> somehow
> be plugged into a
> choreography and magically conform to the choreography rules. However I
> believe that
> it should be possible to use standard wsdl with no special choreo 
> extensions
> or
> interfaces. Is this what you mean Frank?
>
> Martin.
>
>> -----Original Message-----
>> From: Burdett, David [mailto:david.burdett@commerceone.com]
>> Sent: Friday, September 05, 2003 2:58 PM
>> To: 'jdart@tibco.com'; Francis McCabe
>> Cc: Burdett, David; 'Monica Martin'; 'Martin Chapman'; 'Yves
>> Lafon'; 'Ugo Corda'; 'Cummins Fred A'; public-ws-chor@w3.org
>> Subject: RE: Correlation Requirements
>>
>>
>>>>> There may even be a set of services that you want to
>> coordinate in a
>> particular fashion to achieve a particular goal (e.g., the
>> warehouse, credit card, delivery services combine to deliver
>> a book.)<<<
>>
>> In this case aren't you just defining a business process over
>> which you have total control where you are just using the
>> existing services within their already pre-defiined constraints?
>>
>> If this is true you don't need a CDL and the services you use
>> don't need to be changed to become choreography aware - i.e. I agree.
>>
>> But that's not the problem I am thinking of.
>>
>> Let's suppose a seller has a service that can accept orders.
>> When the service receives the order it needs to know how to
>> respond, and, also know what types of messages the buyer
>> might send next. As I said in my earlier email we have
>> identified 14 different ways of placing an order.
>>
>> As I see it, there two ways you *could* solve this problem:
>> 1. Define 14 different services where each one corresponds to
>> a different way of doing business, or 2. Define 1 service
>> that is choreography aware where each message sent identifies
>> in some way the choreography that is being followed.
>>
>> I prefer the second approach for solving *this* problem as it
>> is easier to manage and easier to re-use existing services in
>> new and novel choreographies as you don't need new service
>> definitions ... at least that is the way I see it.
>>
>> I am not actually disagreeing with anything you're saying. I
>> just think that there are basically two types of problems
>> here: 1. Where a single entity (e.g. a business) is designing
>> a process that is using existing services in their standard
>> ways in this case a CDL or choreography aware services is not
>> needed 2. Where two or more entities need to use one or more
>> of their existing services in various different ways and they
>> need to know which variation to follow - this is where a CDL
>> and a way of identifiying it in a message is useful.
>>
>> David
>>
>> -----Original Message-----
>> From: Jon Dart [mailto:jdart@tibco.com]
>> Sent: Friday, September 05, 2003 1:29 PM
>> To: Francis McCabe
>> Cc: Burdett, David; 'Monica Martin'; 'Martin Chapman'; 'Yves
>> Lafon'; 'Ugo Corda'; 'Cummins Fred A'; public-ws-chor@w3.org
>> Subject: Re: Correlation Requirements
>>
>>
>>
>> +1.
>>
>> The description of particular service requirements and
>> capabilities is
>> generally in WSDL, or in WS-Policy, which can be viewed as a
>> supplement
>> to WSDL, not at the choreography layer. The set of such
>> requirements and
>> capabilities is expanding all the time.
>>
>> BPEL hasn't placed correlation-related requirements on
>> services, either,
>> but has provided a mechanism through which business processes can
>> specify what the correlation mechanism is, in a flexible way that is
>> conformable with multiple emerging specs in this area.
>>
>> --Jon
>>
>> Francis McCabe wrote:
>>> A given service will have its *way* of doing things. That
>> may, or may
>>> not
>> be, fully described in a choreography document. There may
>> even be a set of services that you want to coordinate in a
>> particular fashion to achieve a particular goal (e.g., the
>> warehouse, credit card, delivery services combine to deliver
>> a book.) Each of these (say) does its thing in a rich way, and
>> *I* want to document how to use them to achieve the book
>> delivery service - I should be able to do that in a CDL
>> without impacting any of the existing services. A corollary
>> of that is that there may be no way of determining what
>> choreography a given message is part of (by looking at the
>> messages), it is simply an interpretation of the CDL.
>>
>>
>>
>>
>
Received on Monday, 8 September 2003 14:05:52 GMT

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