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Web architecture and specification overlap

From: Graham Klyne <GK@NineByNine.org>
Date: Mon, 07 Jan 2002 13:27:40 +0000
Message-Id: <>
To: www-tag@w3.org
At the December 2001 IETF meeting, I engaged in a discussion about how some 
well-established Internet "access" protocols might look if they were mapped 
to use XML for their basic protocol-unit structure (think of IMAP, ACAP, 
LDAP, etc.).

The person with whom I was talking had considered that XSLT might be a 
common basis for selecting information to be accessed -- currently, these 
protocols all have their own ad-hoc way of doing this.  (Of these, I think 
that LDAP has a relatively clean access-specification model.)  And, yes, I 
can see that XSLT *could* be used in this way, even if (a) it's not at all 
what XSLT has been designed to do, and (b) it is seriously overkill for the 
task in hand.  My response was to consider XQuery for the same purpose, and 
subsequent perusal of its specification draft did seem to indicate that it 
was about right for the purpose being explored.

So what's this to do with Web architecture?

It struck me that a very experienced protocol designer had managed to pick 
the "wrong" XML tool for the job.  It also seems to me that there is an 
architectural difficulty when there are different tools in the XML family 
that can be adapted to perform the same function.  (To be fair, there are 
mitigating considerations:  (a) both of the tools make heavy use of the 
common XPath specification, which provides much of the needed 
functionality, and (b) XQuery is not yet out of working draft status, so 
might easily be overlooked.)

But the overlap of functionality remains, and I think this is something 
which we would prefer to avoid in the overall Web architecture.  For 
example, I could imagine a variant of XSLT being specified as a wrapper 
around one or more XQuery expressions.

This is an observation, and I don't really think that we should try to do 
anything about XSLT/XQuery at this stage.  But I think it illustrates a 
kind of issue to which I hope the TAG can be sensitive, and provide some 
early guidance to build web architecture as a neat tessellation of 
interlocking pieces, rather than ending up with a tangle (I was tempted to 
say "web") of significantly overlapping specifications.


       /\ \    Graham Klyne
      /  \ \   (GK@ACM.ORG)
     / /\ \ \
    / / /\ \ \
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Received on Monday, 7 January 2002 08:48:55 UTC

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