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Re: Summary of the QName to URI Mapping Problem

From: Piotr Kaminski <pkaminsk@home.com>
Date: Wed, 15 Aug 2001 17:07:16 -0700
Message-ID: <00fc01c125e7$84425fa0$35254d18@gv.shawcable.net>
To: <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


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.


Yet, using the standard concatenation mapping, both QNames are mapped to the
same URI:


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.

        -- P.

  Piotr Kaminski <piotr@ideanest.com>  http://www.ideanest.com/
  "It's the heart afraid of breaking that never learns to dance."
Received on Wednesday, 15 August 2001 20:04:04 UTC

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