RE: Definition of Choreography

> -----Original Message-----
> From: Mark Baker [mailto:[email protected]]
> Sent: Thursday, October 17, 2002 9:06 AM
> To: Champion, Mike
> Cc: [email protected]
> Subject: Re: Definition of Choreography
> 
> 

> But David said something that suggested that it was defining 
> the *how*,
> not just the *what*; "specification of ordering of messages".  If it
> were to define the *what*, I would expect it to say something like;
> "The specification of potential state changes".

OK, I guess I'll propose a revision of David's definition:

"Web Services Choreography" is the description of a set of messages that can
be seen as defining a composite web service. The focus is on "what": the
identity of the messages, the state changes implied by various messages, and
the means of maintaining/exchanging state across a collection of nodes, and
not the definition of turing complete logic to determine the actual sequence
of messages. It's practical value is as a formal definition of a "policy"
about the individual services that must be invoked and the state changes
that they must produce in order to produce a composite result.

Still pretty tentative.  I'm not sure whether we need the "from the
perspective of one node or a collection of nodes" bit.  Maybe ...

We should probably also couple it with a definition of "Orchestration"
(and/or some synonym):

"Web Services Orchestration" is a definition of the logic by which a web
services Choreography is executed, in some Turing-complete language."   The
focus is on "how" to determine the precise sequence and content of messages
in a composite web service, under the declarative constraints defined by a
Choreography. Its practical value is as an executable business process /
workflow.

Again, this is just a way of factoring out this stuff that makes sense to
me.  Not sure if people who know what they're talking about agree :-)  

Please critique!