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Re: Summary: Section 2: What does a URI identify?

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Tue, 19 Mar 2002 08:38:25 +0000
Message-Id: <5.1.0.14.0.20020319081058.00aa6338@0-mail-1.hpl.hp.com>
To: Paul Grosso <pgrosso@arbortext.com>, "Jonathan Borden" <jonathan@openhealth.org>, <www-tag@w3.org>
At 14:20 18/03/2002 -0600, Paul Grosso wrote:
[...]

>No!  People keep getting this wrong, and unfortunately major browsers
>do too which is really making a mess of the use of base URLs to the
>point where one cannot use <base> and <a href="#xxx"> sorts of references
>together, because this misinterpretation of #xxx refs with respect to
>base URL destroys the ability to maintain intradocument xrefs.

That looks like an eminently reasonable requirement for HTML.

Let me explain what RDF is trying to accomplish.

For good or ill, RDFCore has inherited a situation where:

   <rdf:Resource rdf:ID="foo">

names a resource whose URI is <base-uri>#foo, i.e. it is relative to the 
document containing the element.

These relative references cause problems.  One of the most frequent newbie 
errors with DAML+OIL I have seen is "I have tried processing 
http://www.daml.org/example.daml[*], and it didn't work right."  The reason 
is that the user should be using 
http://www.daml.org/example.  http://www.daml.org/example.daml contains 
exactly the same text, but because it contains these pesky relative 
references using rdf:ID, the  URI's generated by the parser are wrong.

I first came across this problem when I copied the RDF schema to my hard 
drive so I could work on some code on a plane.  I was a little surprised to 
find I had uri's of the form:

   file:c:\temp\rdfschema.rdf#Class

What is needed is a way to specify, in the XML document, a base for 
converting relative URI references to absolute form.  Then it would not 
matter, where the file was accessed from.

The other obvious use case is where the RDF in question has no obvious URI, 
e.g. when it is generated as part of protocol, perhaps for e.g. in cc/pp.

Whilst the RDF community could invent its own mechanism for this, further 
divergence of RDF from XML does not seem like a good thing.  We have 
decided therefore, to test whether we can use xml:base for this purpose.

It seems that HTML and RDF have different goals here.  I wonder if there is 
a way to reconcile them.

Brian

ps: It would to keep clearly separate in our minds, the issue of what does 
a URI (reference) identify and the use of xml base.

[*] the actual uri given here is incorrect but illustrates the point in 
less space.
   
Received on Tuesday, 19 March 2002 03:47:43 GMT

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