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Re: Summary of the QName to URI Mapping Problem

From: pat hayes <phayes@ai.uwf.edu>
Date: Thu, 16 Aug 2001 12:55:41 -0700
Message-Id: <v04210107b7a1d42cc19a@[130.107.66.237]>
To: "Piotr Kaminski" <pkaminsk@home.com>
Cc: www-rdf-logic@w3.org
>Dan Connolly said:
> > The RDF spec includes an unambiguous QName -> URI mapping:
> > uri(qname) = concat(nsname(qname), localname(qname))
>
>The mapping mechanism is indeed unambiguously defined.  It can, however,
>lead to invalid results.
>
>Let's start from the following axioms.
>1.  A QName identifies a (single) resource.
>2.  A URI identifies a (single) resource.
>3.  The goal of a QName -> URI mapping is to transform a QName into a URI
>that identifies the *same* resource.
>
>The above mapping doesn't achieve the goal.  An example follows that is
>essentially equivalent to Patrick's, but I have a feeling that most of the
>contention will be about the axioms above, especially (1).  One could take
>the position that a QName is a purely syntactic construct, and doesn't
>identify anything in and of itself.  I believe such an interpretation
>contradicts the XML Namespaces recommendation, in spirit if not in letter.
>
>Informal example to demonstrate why the mapping is flawed according to the
>axioms:
>
>xmlns:foo="http://ideanest.com/foo"
>xmlns:bar="http://ideanest.com/foobar"
>
>Then the following two QNames identify distinct resources; they do so
>because they are different names, the namespace URI is mine, and I say that
>the resources they identify are different.

This seems to me to be the basic issue: who has the authority to say 
they are distinct?

Suppose someone were to reply: you can SAY that, but if you do say 
it, you are uttering a contradiction, since I can prove you wrong (by 
mapping the Qnames to URIs using the published RDF rules). After all, 
you can *say* (P and (not P)) as well, but I'm not obliged to believe 
you if you do.

>foo:barcat
>bar:cat
>
>Yet, using the standard concatenation mapping, both QNames are mapped to the
>same URI:
>
>http://example.com/foobarcat
>
>While this URI identifies some resource (by definition), it cannot identify
>both of the (distinct!) resources identified by the two QNames
>simultaneously.  Hence the mapping is deficient.

If they really were distinct, that is. Or, you could take the 
position that the use of the mapping shows that they couldn't have 
been distinct.

Pat Hayes

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Received on Thursday, 16 August 2001 15:55:03 GMT

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