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rdfs:Datatype question

From: pat hayes <phayes@ai.uwf.edu>
Date: Fri, 1 Nov 2002 20:25:53 -0600
Message-Id: <p05111b57b9e8e1936836@[65.217.30.130]>
To: w3c-rdfcore-wg@w3.org

Er...guys, Something must have been decided over the summer that I 
missed somehow. As far as I can see, given the decisions we have made 
about datatyping, there simply is no useful role for rdfs:Datatype. 
We don't need it, so why have we got it?

As I understand the current decision, the *only* place that a 
datatype URI can be used so as to exhibit, as it were, its datatyping 
potential , is inside a typed literal. We aren't going to have any 
special datatyping entailments which involve the use of a datatype 
URI as a property (checked in my last email: consensus apparently 
that have agreed not to do that); there are no long-range datatyping 
entailments, for sure, so that there is nothing that can be inferred 
about any interpretations of literals from any reference to a 
datatype class (that is, something can be said to be in the class, of 
course, but the fact that it is a *datatype* class has no particular 
semantic significance for anything else.) And as far as I can see, 
there is no way to infer that anything is in a datatype class, since 
the only things that we know are in those classes are literals, which 
can't be subjects. So we really don't need to impose any special 
datatyping conditions at all on the property or class extensions of 
datatype URIs in any interpretation, even in 
RDFS-with-datatype-entailment.

Given this, I can't quite see what Im supposed to say about 
rdfs:Datatype in the model theory. Like, it's the class of datatypes. 
But that class isn't defined by RDF(S), and its not even known to 
RDF(S), so why has RDFS got a special syntax for it? I don't even 
have any way to refer to it in the MT metalanguage. Time was, when we 
had datatyping banners unfurled all over the place, that we needed 
RDFS to be able to 'declare' that some URIref was supposed to be a 
datatype label, so as to trigger all those range-datatype inferences 
and so on. But now its obvious from the syntax which urirefs are 
supposed to be datatypes: the ones inside the typed literals. Saying 
it in an explicit triple doesn't seem to add anything. And if we say 
it is, and in fact it isn't (or an RDF engine can't find it) then we 
are (or the engine is) in just the same pickle as if we had used it 
inside a typed literal and in fact it isn't. No amount of RDF 
triple-asserting is going to magically create a non-existent datatype.

Unless Im missing something, therefore, I propose that we drop rdfs:Datatype.

PROPOSE: do not introduce rdfs:Datatype into the rdfs namespace.

Then I can put our very simply boiled-down datatyping into the core 
RDF MT quite happily, since it won't involve the RDFS vocabulary in 
any way.  It will just be one extra line in the semantics of 
literals. And if we do keep it, then (unless I am warned of a mistake 
in the above), I am just going to say that it is like rdf:List, 
rdf:seeAlso, rdf:first, rdf:rest, rdf:nil and rdf:comment in having 
no semantics at all.

Pat
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Received on Friday, 1 November 2002 21:26:38 EST

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