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Re: Datatype was RE: Confusion about Collections

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Tue, 26 Nov 2002 15:09:35 +0200
Message-ID: <001c01c2954d$117c89b0$4b9316ac@NOE.Nokia.com>
To: "ext Shelley Powers" <shelleyp@burningbird.net>, <fmanola@mitre.org>
Cc: <www-rdf-comments@w3.org>, "Brian McBride" <bwm@hplb.hpl.hp.com>



[Patrick Stickler, Nokia/Finland, (+358 40) 801 9690, patrick.stickler@nokia.com]


----- Original Message ----- 
From: "ext Shelley Powers" <shelleyp@burningbird.net>
To: "Patrick Stickler" <patrick.stickler@nokia.com>; <fmanola@mitre.org>
Cc: <www-rdf-comments@w3.org>; "Brian McBride" <bwm@hplb.hpl.hp.com>
Sent: 26 November, 2002 14:54
Subject: RE: Datatype was RE: Confusion about Collections


> > 
> > 
> > 
> > [Patrick Stickler, Nokia/Finland, (+358 40) 801 9690, 
> > patrick.stickler@nokia.com]
> <snip>
> 
> > > >
> > > > Shelley,
> > > >
> > > > You can specify the datatype range of a property using rdfs:range to
> > > > accomplish this. E.g.
> > > >
> > > >    my:dateProperty rdfs:range xsd:date .
> > > >
> > > > And this asserts that all values of my:dateProperty are expected
> > > > to be of type xsd:date.
> > > >
> > > > Cheers,
> > > >
> > > > Patrick
> > > 
> > > 
> > > That's good to know Patrick. I must have missed this in the 
> > vocab document.
> > > And one can also assume, then, that people who create instances of a
> > > vocabulary (a specific document) can't override the data type 
> > that's shown
> > > in the schema. Is that correct?
> > 
> > In a sense, yes, in that if they do they will introduce a contradiction
> > into the graph. But this is of course true of any RDF range, not just
> > for datatyping. E.g. if one asserts that
> > 
> >    my:property rdfs:range foo:Blargh .
> > 
> > and someone else asserts
> > 
> >    my:property rdfs:range bar:Foodle .
> > 
> > and if it is known (e.g. by OWL assertions) that the classes
> > foo:Blargh and bar:Foodle have disjunct membership, then there
> > arises a conflict between the two range assertions, and its
> > resolution will likely be based on some concept of authority
> > (though RDFS doesn't explicitly say how to do this).
> > 
> > Likewise, if one asserted
> > 
> >    my:property rdfs:range foo:Blargh .
> > 
> >    some:Thing my:property _:x .
> >    _:x rdf:type bar:Foodle .
> > 
> > then an RDF reasoner may infer
> > 
> >    _:x rdf:type foo:Blargh .
> > 
> > then again if the two classes have disjunct membership, these two 
> > type assertions  for _:x conflict with each other and that
> > conflict may be used by an application as the basis for type
> > checking, taking the explicit range assertion as primary.
> > 
> > Note that with RDF datatyping
> > 
> >    some:Thing some:property "LLL"^^some:Datatype .
> > 
> > implies
> > 
> >    "LLL"^^some:Datatype rdf:type some:Datatype .
> > 
> > though we can't actually express the latter as literals are not allowed
> > to be subjects, but the semantics are "understood" -- i.e. that 
> > the thing denoted by a typed literal node is a member of the
> > value space (the class extension) of the datatype class specified
> > in the typed literal.
> > 
> > I hope the above is helpfull.
> > 
> > Cheers,
> > 
> > Patrick
> > 
> Yes, Patrick. This has been very helpful. I appreciate your clarification.
> 
> Shelley
> 
> P.S. Is this same discussion in the documents, and did I just miss it? 

It's here and there. Though it probably could be made more explicit.

Have a look at the Primer draft, section 5.2

http://www.w3.org/TR/rdf-primer/#properties

and the RDF Vocabulary Description Language (RDF Schema) draft, the
section titled "rdfs:range" (no section numbers in that draft yet, 
unfortunately)

http://www.w3.org/TR/rdf-schema/#ch_range

Though, yes, the relationship between rdfs:range and rdfs:Datatype's
could be made more explicit in the primer. I see that Frank has a note
there to add more about this, so hopefully we'll see this eventually.

Cheers,

Patrick
Received on Tuesday, 26 November 2002 08:09:43 GMT

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