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Re: pfps-04 (why the thread is germane to pfps-04)

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 25 Jul 2003 09:27:20 -0400 (EDT)
Message-Id: <20030725.092720.129614831.pfps@research.bell-labs.com>
To: bwm@hplb.hpl.hp.com
Cc: duerst@w3.org, jjc@hplb.hpl.hp.com, phayes@ai.uwf.edu, www-rdf-comments@w3.org

From: Brian McBride <bwm@hplb.hpl.hp.com>
Subject: Re: pfps-04 (why the thread is germane to pfps-04)
Date: 25 Jul 2003 14:00:31 +0100

> On Fri, 2003-07-25 at 12:54, Peter F. Patel-Schneider wrote:
> [...]
> > Two XML literals are (now) equal in RDF precisely when their Exclusive
> > XML Canonicalizations are the same octet sequence.
> > 
> > However other answers are harder to determine.
> > 
> > 1/ When is an XML literal equal to a plain RDF literal?  A plain RDF
> > literal is a Unicode string (sequence of Unicode characters), so this
> > question boils down to whether octets and Unicode characters are disjoint.
> > I found it difficult to answer this question, because of hints in the
> > exclusive canonicalization document that they are not.
> I think we've established that UNICODE characters and octet sequences
> are disjoint.  Martin, chair of the I18N group confirmed this in:
> http://lists.w3.org/Archives/Public/www-rdf-comments/2003JulSep/0069.html
> Whilst Martin does not like the RDFCore design, as currently specified
> in the ed's drafts, XMLLiterals and plain literals are disjoint.
> Pat has agreed to remove some misleading text, as noted in
> http://lists.w3.org/Archives/Public/www-rdf-comments/2003JulSep/0067.html
> > 
> > 2/ When is an XML literal equal to an XML Schema string? 
> As currently defined, never.  xsd:string's are not octet sequences, see
> http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2003Jul/0043.html
> Peter, how are we doing on pfps-04.  Have we resolved your comment?
> Brian

I believe that a complete theory of equality for XML literals resolves this
comment.  I suggest that several test cases be added to the RDF test suite.

The related issue of whether the value spaces of xsd:string and plain
literals are disjoint also appears to be well on the way to resolution.  It
is less urgent that the related issue of whether the values spaces of
xsd:decimal and xsd:float, but this should also be addressed somewhere,
perhaps only as a test case.


PS: Although the current situation may be technically satisfactory in this
area, the pain in getting there suggests that a slightly different
description of XML literals might be more useful, perhaps something along
the line of making the value space of XML literals in RDF be some abstract
set with equality defined as per exclusive XML canonicalization and
explicitly determined to be disjoint from the value space of plain RDF
literals and also from the XSD value spaces.  This would also probably make
the XML guys much more happy.
Received on Friday, 25 July 2003 09:27:43 UTC

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