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Re: RDF Review

From: pat hayes <phayes@ihmc.us>
Date: Thu, 2 Oct 2003 20:47:39 -0500
Message-Id: <p06001f05bba284fc0680@[10.0.100.25]>
To: Ian Horrocks <horrocks@cs.man.ac.uk>
Cc: www-webont-wg@w3.org, Jeff Pan <panz@cs.man.ac.uk>

>Dear All,
>
>Jeff and I (mostly Jeff) have looked at the latest RDF MT, in
>particular the Datatypes section. We did not have time for an
>exhaustive review, but here are some comments:
>
>Regards, Ian
>========================================

Further to my last message, here is a proposed text for the relevant 
part of section 7. This effectively defines 'datatype clash' more 
broadly to cover all the various cases, including the ill-formed 
literal cases.

----------------------

If the datatypes in the datatype map D impose disjointness conditions 
on their value spaces, it is possible for an RDF graph to have no 
D-interpretation which satisfies it. For example, XML Schema defines 
the value spaces of xsd:string and xsd:decimal to be disjoint, so it 
is impossible to construct a XSD-interpretation satisfying the graph

<ex:a> <ex:b> "25"^^xsd:decimal .
<ex:b> rdfs:range xsd:string .

This situation could be characterized by saying that the graph is 
XSD-inconsistent, or more generally as a datatype clash. Note that it 
is possible to construct a satisfying rdfs-interpretation for this 
graph, but it would violate the XSD conditions, since the class 
extensions of I(xsd:decimal) and I(xsd:string) would have a nonempty 
intersection.

Datatype clashes can arise in several other ways. For example, any 
assertion that something is in both of two disjoint dataype classes:

_:x rdf:type xsd:string .
_:x rdf:type xsd:decimal .

or that a property with an 'impossible' range has a value:

<ex:p> rdfs:range xsd:string .
<ex:p> rdfs:range xsd:decimal .
_:x <ex:p> _:y .

would constitute a datatype clash. A datatype clash may also arise 
from the use of a particular lexical form, for example:

<ex:a> <ex:p> "2.5"^^xsd:decimal .
<ex:p> rdfs:range xsd:integer .

or by the use of an ill-typed lexical form:

<ex:a> <ex:p> "abc"^^xsd:integer .
<ex:p> rdfs:range xsd:integer .

Datatype clashes are the only inconsistencies recognized by this 
model theory ; note however that datatype clashes involving XML 
literals can arise in RDF and RDFS.

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Received on Thursday, 2 October 2003 21:47:42 GMT

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