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Re: does RDF require understanding all 82 URI schemes?

From: David Megginson <david@megginson.com>
Date: Thu, 8 Feb 2001 12:54:52 -0500 (EST)
Message-ID: <14978.56684.295518.905294@localhost.localdomain>
To: Dave Beckett <dave.beckett@bristol.ac.uk>
Cc: www-rdf-interest@w3.org
Dave Beckett writes:

 > I feel it might be needed for serialisation of the RDF graph to
 > RDF/XML, but I haven't implemented that yet.

Unfortunately, the serialization of an RDF graph is impossible in the
general case: the XML Namespaces spec describes two-part names, but
RDF treats them as single part names, and the act of combining the two
is lossy.  Consider:

  <rdf:Description rdf:about="urn:xxx:001" xmlns:foo="http://www.foo.com/ns">
   <foo:name>David</foo:name>
  </rdf:Description>

The RDF data model sees the triple

  http://www.foo.com/nsname
  urn:xxx:001
  "David"

How can you serialize that back to XML?  This isn't an abstract
problem; the Namespace for the XML Schema datatyping is

  http://www.w3.org/1999/XMLSchema-datatypes

and the Namespace for the magic "xml" prefix is

  http://www.w3.org/XML/1998/namespace

That means that the data type for a decimal number in RDF's view is

  http://www.w3.org/1999/XMLSchema-datatypesdecimal

and xml:lang in RDF's view is

  http://www.w3.org/XML/1998/namespacelang

Ouch!  Fortunately, neither of these is likely to be used as a
property name, but other similar ones likely will be.  We can
hard-code some into RDF processors, but in the general case, we have a
very bad mess on our hands.


All the best,


David

-- 
David Megginson                 david@megginson.com
           http://www.megginson.com/
Received on Thursday, 8 February 2001 12:56:58 GMT

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