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Re: RDF Review

From: pat hayes <phayes@ihmc.us>
Date: Thu, 2 Oct 2003 20:47:33 -0500
Message-Id: <p06001f04bba27ee498d1@[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:


Thanks, guys.

>
>Regards, Ian
>========================================
>
>1. Interpretations
>
>IP no longer (explicitly) a subset of IR (see defn of RDF simple
>interp in Sec 1.3)? Not sure if this has any impact on OWL (or on RDF
>come to that).

I think not, since the old constraint applies to all RDF (and up) 
interpretations.

>
>2. Datatypes
>
>My main impression is that the "datatype clash" in RDF has not
>been defined/explained clearly enough in section 5, which presents the
>datatype interpretation of RDF. Datatype clash is important
>because it is one of *only three inconsistencies* recognized by the
>model theory (see section 5). Until the picture is clear, it is
>difficult to determine how it affects OWL.
>
>When explaining datatype clash, the semantic doc says
>
>"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."

Perhaps the wording of this could be improved and expanded a little, I agree.

>
>However, it is also possible that the problem comes from the lexical
>form, e.g.
>
><ex:a> <ex:b> "2.5"^^xsd:decimal  (1)
><ex:b> rdfs:range xsd:integer  (2)
>
>Is this a datatype clash?

Yes, because of the disjointness of xsd:integer and any non-integer 
values in xsd:decimal.

>
>The only example in section 5 about datatype clash is about typed
>literals, what about the cases that we don't use typed literal. E.g.
>
><ex:c> rdfs:range xsd:string    (3)
><ex:c> rdfs:range xsd:integer    (4)
><ex:d> <ex:c> _:xxx    (5)
>
>Is this a datatype clash?

Yes, since the value spaces of the datatypes are disjoint.

>According to the informative entailment
>rules in section 7, it is a datatype clash:
>
>from (3) and (rdfs3) we have _:xxx rdf:type xsd:string     (6)
>from (4) and (rdfs3) we have _:xxx rdf:type xsd:integer    (7).
>
>If this is the case, does it mean that the informative part of the
>document implies something that isn't mentioned in the normative
>semantics?

No.

>
>The above example can be regarded as property inconsistency; similarly
>we can have class inconsistency:
>
><ex:e> rdfs:subClassOf xsd:integer    (8)
><ex:e> rdfs:subClassOf xsd:string    (9)
>
>means that ex:e is equivalent to owl:Nothing, and adding
>
>_:yyy rdf:type <ex:e>    (10)
>
>leads to ontology inconsistency.

That is true, and I should probably insert some more explanatory text 
to draw attention to these cases. Thanks for shining a light on this 
issue.

It may be impossible to make these changes before LC2, as our 
timetable is now extremely tight, but if not then I will undertake to 
insert some explanatory prose during the LC process before 
publication.

I think this can reasonably be regarded as editorial changes to the 
exposition, since it only seeks to clarify an existing situation.

Pat




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Received on Thursday, 2 October 2003 21:47:35 GMT

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