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RE: Definition of Choreography

From: Burdett, David <david.burdett@commerceone.com>
Date: Fri, 18 Oct 2002 16:58:17 -0700
Message-ID: <C1E0143CD365A445A4417083BF6F42CC053D13D4@C1plenaexm07.commerceone.com>
To: "'Champion, Mike'" <Mike.Champion@softwareag-usa.com>, www-ws-arch@w3.org

Mike

Some observations on WSCI, BPEL4WS and choreographies.

Having reviewed WSCI and BPEL4WS, they both tend to focus on how to sequence
processes to carry out a particular activity. As such they tend to focus on
"private" processes within the enterprise.

What I don't think they do so well, is describe the public processes, often
described as choreograhpies, that **constrain** what a private process can
do when interacting with services outside of its direct control.

I think this is an important distinction as:
1. Public processes need to be standardized, private ones do not.
2. Anything that needs to be standardized should have a formal way of being
defined as an aid to understanding and therefore interoperability

You also need to distinguish between the generic implementation of a
standardized process/choreography and an individual actual implementation.

A generic choreography definition just needs to say, for example, ... "if
you send me an "order" then you must send me an "order response" back - and
really nothing more".

I could have said, but didn't ... "if you send me a RosettaNet Order
contained as an PKCS7 encrypted attachment on a "SOAP with attachments"
message to this URL using HTTP, then I will send you a RosettaNet Order
Response in the same format to the URL you specify in return".

It's all to do with layering. The generic choreography is a universal
business pattern that is independent of how it is implemented, and
specifically the service that implements it. If the only way you can define
a choreography is as part of defining an actual instance then you will get
unnecessary **massive** duplication of choreography definitions.

David

-----Original Message-----
From: Champion, Mike [mailto:Mike.Champion@softwareag-usa.com]
Sent: Friday, October 18, 2002 3:12 PM
To: www-ws-arch@w3.org
Subject: RE: Definition of Choreography





> -----Original Message-----
> From: Mark Baker [mailto:distobj@acm.org]
> Sent: Friday, October 18, 2002 3:45 PM
> To: Cutler, Roger (RogerCutler)
> Cc: 'Dave Hollander'; Burdett, David; 'Mark Baker'; Champion, Mike;
> www-ws-arch@w3.org
> Subject: Re: Definition of Choreography
> 
> 
> Another +1 from me.  Let's see some use cases that 
> demonstrate why it's important to expose choreographies.  
> Because as we've seen from these
> specs, they're not exactly simple, and if you can accomplish something
> without needing to agreeing to new stuff, that reduces coordination
> costs (read; reduces cost of doing business).

I really, really hope we can stay focussed on identifying the components,
connectors, and data that are identified by the BPEL4WS and WSCI specs,
determine which of these are important to cover in a Choregraphy spec, and
write this up in a way that makes a good case to the W3C AC for chartering a
WG to define such a spec.  That's what we've agreed to do at the F2F and in
response to the request for a tighter scope by the WS CG.  Use cases would
definitely help in that effort, and I think the "Definition of Choreography"
thread has gotten some ideas going.

A "devil's advocate" position that this isn't needed is very useful in
sharpening our arguments, and Mark does SUCH a good job at it :-)  Still,
let's not get too distracted by arguing for or against the idea that a
Choreography spec is needed -- we already decided that it is! -- and focus
on defining what exactly the scope of a Choreography WG would be.  When we
have a better handle on that, getting pushback helps us make the case, and
gets the counter-arguments on the record for the AC's use.

To put it another way, I'll feel that we've done our job if we analyze WSCI
and BPEL from the WSA framework, make the best case for a new WG, but the AC
disagrees.  I will NOT feel that we've done our job if we spend the next
month arguing about whether to do the analysis or not and then offer nothing
to help the AC make their decision.
Received on Friday, 18 October 2002 19:58:18 GMT

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