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Re: Definition of Choreography

From: Mark Baker <distobj@acm.org>
Date: Thu, 17 Oct 2002 21:15:00 -0400
To: "Champion, Mike" <Mike.Champion@SoftwareAG-USA.com>
Cc: www-ws-arch@w3.org
Message-ID: <20021017211500.M27626@www.markbaker.ca>

On second thought, I'd like to focus on this part of your response,
Mike;

On Wed, Oct 16, 2002 at 09:50:12PM -0400, Champion, Mike wrote:
> reason = prompt("why are you doing this to yourself?")
> destination = prompt("where are you going")
> departure = prompt("when do you leave")
> return = prompt("when do you return")
> tripId = TentativelyBookTravel(destination, departure, return)
> estimatedCost = getCost(tripId)
> if (estimatedCost > managerApprovalLimit)
>    approved = getVPApproval(reason, estimatedCost)
> else
>    approved = getManagerApproval(reason, estimatedCost)
> if (approved)
>   confirmTrip(tripId)
> else
>   cancelTrip(tripId)

This is a good example.  And one could certainly specify a language for
describing such a flow of operations.  But why is a *standardized*
language required?  Why would I ever need to *share* a description with
anybody?

As I see it, that flow (minus conditions, which are encapsulated within
the service) can be observed at runtime, so doesn't need to be specified
earlier, at least for interop reasons.  So I invoke "prompt()" on the
first service, which returns "why are you doing this to yourself?",
which I answer by invoking "answer('because I feel like it')".  The
response to that invocation is then another question, or perhaps a
pointer to the next service which I invoke prompt() on, etc, etc..

Behind the scenes, I could certainly be using some description language
to drive this flow.  But again, why does it matter if it's standardized
or not?  The only reason I could think of, is because we're trying to
enable somebody to reuse their rules with different tools.  But that
seems quite different than the motivation I've seen for some of the
choreography specs out there.  For example, all of them integrate with
WSDL, which suggests that choreography is part of the interface, not
just the implementation.

Can anybody shed some light on this?

MB
-- 
Mark Baker, CTO, Idokorro Mobile.  Ottawa, Ontario, CANADA.
http://www.markbaker.ca             http://www.idokorro.com
Received on Thursday, 17 October 2002 21:13:29 GMT

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