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Re: RDF and xml:base

From: Dave Beckett <dave.beckett@bristol.ac.uk>
Date: Thu, 10 May 2001 08:42:51 +0100
To: Aaron Swartz <aswartz@swartzfam.com>
cc: Ron Daniel <rdaniel@interwoven.com>, RDF Interest <www-rdf-interest@w3.org>
Message-ID: <1144.989480571@tatooine.ilrt.bris.ac.uk>
>>>Aaron Swartz said:
> The major problem that I see with XML Base is that of
> backwards-compatibility. XML Base can change the entire meaning of an RDF
> document (by changing the URIs). Worse, depending on where in the document
> it is placed, it can add additional triples to the output.
> 
> XML Base (as it rightly should be) is built on the fact that most RDF
> applications ignore, or handle specially, attributes outside their
> namespace. Unfortunately, RDF interprets all namespaces as part of the RDF
> document, and thus many parsers will probably end up creating an extra
> triple for XML Base in certain places. The others will probably choke on the
> syntax error.

RDF does not interpret all namespaces from the RDF/XML syntax - the
XML namespaces spec reserves all namespace prefixes starting 'xml'
for XML use:

  [[Namespace Constraint: Leading "XML" Prefixes beginning with the
    three-letter sequence x, m, l, in any case combination, are
    reserved for use by XML and XML-related specifications.]]
  (end of section 2)

    Namespaces in XML - http://www.w3.org/TR/REC-xml-names/

and XML Base is thus one of these:

  [[The syntax consists of a single XML attribute named xml:base.]]

    XML Base (Proposed REC) - http://www.w3.org/TR/xmlbase/

If any RDF/XML parser does something with the xml:base attribute at
the RDF level - emitting it as a property say - then that is wrong.

This also applies to any other element/attribute with namespace
prefix starting with xml that has no existing RDF/XML interpretation.
The RDF Model and Syntax specification mentions only one of these -
xml:lang but is already an issue for RDF Core:

  Issue rdfms-xmllang: Why isn't xml:lang information represented
    within the RDF data model?
  http://www.w3.org/2000/03/rdf-tracking/#rdfms-xmllang

> If RDF was to use XML Base, it wouldn't go in the work of the current RDF
> Core group (since they're not really supposed to be adding to the spec) so
> it would have to wait for something like RDF 2.0.

More likely since XML Base isn't supported by all XML parsers, and is
about XML syntax rather than RDF modelling, we can wait for it to be
more widely deployed before needing an interpretation.  The
interpretation would be along the lines pointed out by Ron Daniel in
http://lists.w3.org/Archives/Public/www-rdf-interest/2001May/0116.html

Dave
Received on Thursday, 10 May 2001 03:43:06 GMT

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