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Re: Quick review of RDF primer

From: Frank Manola <fmanola@mitre.org>
Date: Tue, 03 Dec 2002 12:30:15 -0500
Message-ID: <3DECEA27.13A2ADB9@mitre.org>
To: pat hayes <phayes@ai.uwf.edu>
CC: Graham Klyne <GK@ninebynine.org>, w3c-rdfcore-wg@w3.org

pat hayes wrote:
> 
> >
> >General comment, not specifically Primer:  the description of
> >rdf:value is fine, but how does it relate to a normative
> >specification?  What can we say formally about rdf:value?
> 
> Right now, we say explicitly that it has no particular meaning.
> 
> >What formal semantics (interpretation) allows us to make inferences like:
> >
> >    my:cat rdf:type ex:DomesticCat .
> >    my:cat ex:weight _:x .
> >    _:x rdf:value "15" .
> >    _:x ex:unit ex:Kilogram
> >
> >=>
> >
> >    my:cat rdf:type ex:Obese .
> 
> Nothing in the MT provides any connection in meaning between the
> third and fourth triple of the first graph.

I assume you mean beside the fact that they both have the same subject? 
Anyway, this isn't specific to rdf:value is it?  I mean, you couldn't
make the inference if you'd used a datatype "weightInKilograms" either. 
You'd need much more machinery than RDF has.

> 
> I was under the impression that we had formally decided NOT to
> support this kind of usage. Wasn't that part of the local-datatyping
> no-fancy-idioms decision?
> 
> >but NOT:
> >
> >    my:cat rdf:type ex:DomesticCat .
> >    my:cat ex:weight _:x .
> >    _:x rdf:value "15" .
> >    _:x ex:unit ex:Pound
> >
> >=>
> >
> >    my:cat rdf:type ex:Obese .
> >
> >?
> >
> >My point here is if we are to encourage such usage of rdf:value,
> >then there ought to be some normative description to back up such
> >usage.
> 
> I agree.  Either we should not mention this stuff, or else we should
> back it up with some semantics. 

Well, that doesn't seem to be the principle on which we've been
operating!  If we're going to deal with this, let's do rdfs:isDefinedBy
too!

> It wouldn't be hard to do and it
> would also enable us to do some neat datatyping  entailments that
> people seem to think are obvious, such as (with appropriate
> wellformedness caveats)
> 
> aaa ppp "sss"^^ddd .
> 
> -->
> 
> aaa ppp _:x .
> _:x rdf:value "sss" .
> _:x rdf:type ddd .
> 

Yes, keeping in mind that rdf:value can be used with more complicated
relationships too (i.e., _:x could have multiple properties qualifying
the value, not just a single one).

--Frank

-- 
Frank Manola                   The MITRE Corporation
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Received on Tuesday, 3 December 2002 12:30:24 EST

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