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Re: What is SOAP?

From: Mark Baker <distobj@acm.org>
Date: Tue, 26 Mar 2002 21:19:50 -0500 (EST)
Message-Id: <200203270219.VAA19856@markbaker.ca>
To: jacek@systinet.com (Jacek Kopecky)
Cc: xml-dist-app@w3.org, skw@hplb.hpl.hp.com (Stuart Williams), noah_mendelsohn@us.ibm.com (Noah Mendelsohn), fallside@us.ibm.com (David Fallside), www-ws-arch@w3.org
Hey Jacek,

>  a) an extension of the web (or HTTP), or
>  b) an RPC request/response protocol on top of *a transport 
> layer*, or
>  c) simply a messaging protocol with basically every message
> being one-way (again, on top of a transport layer).
> 
>  I think the original Abstract Model [1] assumed (c), I think
> that many of our audience still (unfortunately) assume (b), and I
> think Mark Baker assumes (a) (at least I haven't noticed another
> strong proponent of (a)). I believe that the majority expectation
> is also (c).

I believe SOAP is c), but that a) is a special case of c) where
the meaning of the message transfer is inherited from HTTP (just to
compare apples-to-apples with your a).

[snip]

>  AFAIK, the history of SOAP is the transition from (b) to (c).  
> I don't think there is a possible transition from (c) to (a)
> other than starting from scratch. And I don't think (a) and (c)  
> can be combined simply and nicely.

IMO, there is definitely a transition.  The chameleon view is about
making this transition, but assigning meaning to the sending of a SOAP
message, where that meaning comes from the method used in the underlying
protocol.  In fact, c) by itself is insufficient with which to get any
work done, because no meaning has yet been assigned to the sending of
the SOAP message.  What most people currently do is put the meaning
within the envelope, such as is done here (not to pick on Gudge, but
this is a simple and illustrative example);

http://www.xml.com/pub/a/2002/02/20/endpoints.html

The example I had in mind is this one;

<soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope">
  <soap:Body>
    <pre:Add xmlns:pre="http://example.org/lists"
     soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding" >
      <person>
        <name>Hayley</name>
        <age>30</age>
      </person>
    </pre:Add>
  </soap:Body>
</soap:Envelope>

Here, we see the meaning of the message "Add" in the message itself.
A chameleon version of this with SOAP/HTTP would be;

<soap:Envelope xmlns:soap="http://www.w3.org/2001/12/soap-envelope">
  <soap:Body>
      <person>
        <name>Hayley</name>
        <age>30</age>
      </person>
  </soap:Body>
</soap:Envelope>

What happened to "Add" and the URI?  Well, HTTP POST roughly means
"Add", and the URI, "http://example.org/lists" is what you POST to.

Any clearer?

MB
-- 
Mark Baker, Chief Science Officer, Planetfred, Inc.
Ottawa, Ontario, CANADA.      mbaker@planetfred.com
http://www.markbaker.ca   http://www.planetfred.com
Received on Tuesday, 26 March 2002 21:14:38 GMT

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