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Re: questions about rdfs:Datatype [Was: RE: Seeking normative definition of datatyping]

From: Frank Manola <fmanola@mitre.org>
Date: Wed, 04 Dec 2002 17:36:57 -0500
Message-ID: <3DEE8389.9070201@mitre.org>
To: Roland Schwaenzl <roland@mathematik.uni-osnabrueck.de>
CC: www-rdf-comments@w3.org


Here's a try at answering your question:

When an RDF processor understands a datatype, the basic requirement is 
that it be able to tell, given a literal and a URIref identifying the 
datatype, whether or not the literal is a valid lexical form for that 
datatype.  The RDF processor may also be able to do additional things, 
depending on how much information it has available (or can get access 
to) about the datatype, such as:

* determine, given two literals from the same datatype, whether they map 
to the same value in that datatype

* determine, given two literals from different datatypes, whether they 
map to the same value (it has to "understand" both datatypes, in that case)

This is covered in Section 3.4 of the RDF Semantics document;  that 
section is currently being expanded somewhat to provide further details.

Based on the amount of "understanding" an RDF processor has of a 
datatype or datatypes, an RDF graph may be extended with extra 
information the processor can deduce via that added understanding (as 
described in the Semantics document), e.g., a subclass relationship 
between datatypes.  However, keep in mind that this "understanding" is 
not defined by RDF;  it must be built into RDF software that reflects 
the meaning of the datatype involved.  You should also note that the 
"understanding"" of a datatype we talk about in RDF is far less than you 
would expect for the "understanding" required for a datatype in a 
programming language (where the set of operations associated with the 
datatype must also be understood).


Roland Schwaenzl wrote:

> The RDF Primer has the sentence:
> "As far as RDF is concerned, you can write any pair of URIref and 
> literal you want as a typed literal"
> In this contex what exactly  is the meaning of 
> "understanding"/recognizing a datatype?
> Could changes result for an RDF Graph, when a processor "understands" a 
> datatype
> (aside from taking RDF MT hulls)?
> Thanks in addvance for clarification,
> rs

Frank Manola                   The MITRE Corporation
202 Burlington Road, MS A345   Bedford, MA 01730-1420
mailto:fmanola@mitre.org       voice: 781-271-8147   FAX: 781-271-875
Received on Wednesday, 4 December 2002 17:19:39 UTC

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