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   Re: [xml-dev] ANN: xpath1() scheme for XPointer

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At 5:09 PM -0600 10/26/02, Uche Ogbuji wrote:

>Wow.  Too bad for content negotiation that in your world differing
>representations MUST have differing URIs.  Too bad for you that the real world
>is much more complex.

Mostly I've stayed out of the whole resource/representation debates 
because it's not totally clear to me why anybody cares about this, or 
exactly what the relevant definitions are to discuss this. Part of 
the problem seems to be disagreements over just what a resource is.

In this context, though, I've been mulling this one or over for a day 
or so, and I think I can defend the position that multiple URIs 
really are called for here, at least by some of the definitions that 
are out there for URI.

First of all, an XIncluded document is not just a different format. A 
GIF and a JPEG image formed from the same digital camera screen shot 
without significant editing containing basically the same 
information. That's why content negotiation might be appropriate in 
that case, or similar. That's why they may have the same URIs, 
because they are the same thing.

With XInclude however, we have two very different documents before 
and after the include:

<html xmlns:xi="http://www.w3.org/2001/XInclude";>
    <xi:include parse="text" href="http://www.example.com/"; />

This is not the same information as contained in the document after 
the include. I don't believe that they're just different 
representations of the same thing. Indeed, with fallbacks, processing 
the same document from different locations may produce radically 
different results. For example, consider a doctor's PDA that's used 
to query a local database to find out if a patient should be 

    <xi:include parse="text" href="http://www.hospital.com?patient=89765";>
        <1-- First do no harm.--> No

Furthermore, consider the most tautological definition of a resource: 
it's what a URI identifies. The pre-include document has a single 
URI. Therefore it's one resource. The post-include document has 
multiple base URIs according to the Infoset that XML is based on. 
Therefore it's several resources, not just one. Indeed since there is 
no one URI that points to the post include document, it's 
questionable whether it's a resource at all. (This is one of the 
things I really don't like about the  tautological definition of a 
resource. To my mind, the post-include document is a resource whether 
it's got a URI or not.)

But bottom line: it sure feels to me that there are different 
resources pre- and post-include. They are not just different 
representations of the same thing.

| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
|          XML in a  Nutshell, 2nd Edition (O'Reilly, 2002)          |
|              http://www.cafeconleche.org/books/xian2/              |
|  http://www.amazon.com/exec/obidos/ISBN%3D0596002920/cafeaulaitA/  |
|  Read Cafe au Lait for Java News:  http://www.cafeaulait.org/      |
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