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[Fwd: RE: Head's up on Intermediaries]

From: Jean-Jacques Moreau <jean-jacques.moreau@crf.canon.fr>
Date: Tue, 02 Dec 2003 16:16:48 +0100
Message-ID: <3FCCACE0.3080203@crf.canon.fr>
To: WSD Public <www-ws-desc@w3.org>

ws-chor is currently having a discussion on intermediaries, and it has 
just been pointed out there is no support for them currently in WSDL.

This may be interesting data when we look at issue 96.


-------- Original Message --------
Subject: 	RE: Head's up on Intermediaries
Resent-Date: 	Sun, 30 Nov 2003 23:10:21 -0500 (EST)
Resent-From: 	public-ws-chor@w3.org
Date: 	Sun, 30 Nov 2003 20:10:07 -0800
From: 	Ugo Corda <UCorda@SeeBeyond.com>
To: 	Francis McCabe <frankmccabe@mac.com>, <public-ws-chor@w3.org>

Hi Frank,

While I agree with you regarding the importance of intermediaries and
the fact that in many cases they should not be overlooked by
choreography, I have a couple of points to make.

>  a service involving intermediaries is a composite service.

I don't think that is necessarily true in the general case.
Intermediaries can perform activities on behalf of the service client,
the service provider or a third party. In the case of intermediaries
working for third parties (e.g. monitoring network traffic) it would not
be very meaningful, in my opinion, to see them as logically part of the
same composite service that includes the actual service.

The second point I want to make is the fact that choreography depends on
WSDL, more than on SOAP, and, unfortunately, WSDL has virtually no
intermediaries support so far. So talking about them through WSDL is
currently quite hard.


     -----Original Message-----
     *From:* public-ws-chor-request@w3.org
     [mailto:public-ws-chor-request@w3.org]*On Behalf Of *Francis McCabe
     *Sent:* Friday, November 28, 2003 10:16 AM
     *To:* public-ws-chor@w3.org
     *Subject:* Head's up on Intermediaries

     Hi y'all
     Just thought that you may want to consider something in the
     choreography space.
     Recently the WSA has been wrestling with intermediaries.

     There are at least two camps here: those who wish that they didn't
     exist and those who think that there might be something interesting
     in them. (Personally I belong to the latter camp).

     An important note to clear up any potential misunderstanding:
     despite the name, intermediaries *do not* imply separate agents
     doing processing of messages.

     What follows is a mixture of speculation and rational reconstruction.

     Intermediaries is an idea proposed in SOAP 1.2 (and therefore is a
     W3C recommendation)

     1. One view of intermediaries is that they *are* separate processing
     entities that focus on messages' headers. A crucial property of this
     view of intermediaries is that the messages that they spit out are
     considered to be the *same* messages that they receive.
     I use the term considered judiciously: outgoing messages are, in
     effect, declared to be equivalent to corresponding input messages.

     This interpretation of intermediaries tends towards a `poor man's
     choreography'; may still be useful but limited in scope.

     2. A second view, partly suggested by the SOAP 1.2 spec itself,
     paints a somewhat grander view. The best way I know of approaching
     this is via structured messages:

     A message has elements which are standardized separately and then
     combined into a whole document. A simple example of this is customer
     authentication: the tokens necessary are captured in a standard
     form, supported within SOAP by means of a standardized header. All
     customer authentications (whatever the purpose of the actual message
     is) are handled in the same way.
     This standardization permits a kind of factoring that is quite
     interesting: the different stakeholders in an organization may wish
     to inspect messages from their particular standpoint and
     standardized headers facilitate that.

     This leads to a kind of architecture for delivering Web services
     that might be called *Document Centric Middleware*: a Web service
     may be delivered via a collaboration of specialized processors that
     each process a particular aspect of a message/document. Many (all)
     of these specialized processors have relatively simple - and
     standardized across the Enterprise -- functions. The 'slave'
     processors may be called *intermediaries* and the 'master' processor
     may be called the *ultimate recipient. *
     * *

     What does this mean for WS-CHOR?

     1. Intermediaries should be taken seriously. They represent a
     powerful way for an enterprise to structure their services in a
     manageable way.
     2. Services can not be regarded as simple monolithic lumps that have
     no internal structure. This is true whether you take the simple
     interpretation or the rich interpretation of intermediaries.
     3. The layered approach to message structure implies that, whether
     we like it or not, we have to address service composition: a service
     involving intermediaries *is* a composite service.


     P.S. Happy Thanksgiving!
Received on Tuesday, 2 December 2003 10:18:05 UTC

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