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Re: Input sought on datatyping tradeoff

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Fri, 12 Jul 2002 09:54:47 +0100
Message-Id: <5.1.0.14.0.20020712094054.02325e78@15.144.25.13>
To: Piotr Kaminski <piotr@ideanest.com>, www-rdf-interest@w3.org
Cc: pat hayes <phayes@ai.uwf.edu>

At 13:43 11/07/2002 -0700, Piotr Kaminski wrote:
>A side comment on the datatype question:
>
>From: "Brian McBride" <bwm@hplb.hpl.hp.com>:
> > Test D:
> >
> >    <Jenny>      <ageInYears> "10" .
> >    <ageInYears> <rdfs:range> <xsdr:decimal> .
> >
> >    <John>  <ageInYears>      _:a .
> >    _:a     <xsdr:decimal>   "10" .
>
>According to RDF Model Theory rules, this means that <xsdr:decimal> is both
>a class and a property.  As far as I can tell this is legal (?),

Yes

>  but is it
>the desired effect?

Yes.  We did at one point in our discussions have different terms for the 
value space (Class) and lexical to value mapping (property) of the 
datatype.  We decided however that it was simpler, and easier for the 
non-expert user, to have just one term to represent the 
datatype.  Fortunately, the way the semantics are defined this works.

>   What does it mean?

Remember, that in the model theory, a class is not a set of things, it is a 
resource which has an associated set, the class extension, which is the set 
of members of the class.  This is how we addressed the issue of Class being 
a member of itself.  A class can be a member of its own extension, and we 
can do that and stick with the most commonly understood set theory.

Similarly a Property is not a set of pairs, but is a resource with a 
property extension which is the set of pairs defining the relation.

A resource can have both a Class extension and a property extension and it 
all works fine (so Pat tells me - I'm not a mathematician).

The way we have defined datatypes, a datatype is a resource which has both 
a class and property extension.  The advantage of doing things this way is, 
as I said above, users need only understand one concept, the datatype and 
don't have to use different names in different contexts.

Pat: feel free to jump in here if I'm getting this wrong.

Brian
Received on Friday, 12 July 2002 04:59:01 GMT

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