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Re: Web services composition

From: Mark Baker <distobj@acm.org>
Date: Tue, 18 Mar 2003 12:39:11 -0500
To: Francis McCabe <fgm@fla.fujitsu.com>
Cc: www-ws-arch@w3.org, public-ws-chor@w3.org
Message-ID: <20030318123911.F15568@www.markbaker.ca>

Hi Frank,

On Sun, Mar 16, 2003 at 09:25:47PM -0800, Francis McCabe wrote:
> According to the WS-choreography charter, and according to the WSA 
> requirements, it is stated that Web services should be recursively 
> composable.

> However, I have to say that this goal appears to conflict with another 
> goal/property of Web services: that a Web service is identified using a 
> URI. (The URI part is not relevant to the following discussion, but the 
> identification bit is.)

Yes, I think some of the feedback that Paul Prescod and I provided to
choreography style solutions reflects that.  REST style composition via
routing enabled by a layered architecture, is much more straightforward
and doesn't have any of these problems AFAIK, as a composite service is
identified by a URI.

For example, I might decide to aggregate Yahoo's stock quote service,
and make the aggregate available via my own URI; a client of my service
has no idea that I route the GET request to yahoo.com, and then perhaps
to Babelfish for translation, and HTML-to-WML converter for a wireless
version, just as I have no idea if Yahoo routes the request elsewhere.
This is the value of the uniform interface, and I've yet to see any
large scale composition occur that didn't follow this pattern, (though
not necessarily with REST's uniform interface, but still with a generic
interface of some sort).

Composition is integration, and integration is always easier when the
things that are being integrated expose the same interface.

So with that said, I think there's another possible solution;

5.  Use routing for composition

Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Web architecture consulting, technical reports, evaluation & analysis
Received on Tuesday, 18 March 2003 12:34:49 UTC

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