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Re: response to issue pfps-09

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Wed, 05 Feb 2003 18:51:41 -0500 (EST)
Message-Id: <20030205.185141.26472231.pfps@research.bell-labs.com>
To: phayes@ai.uwf.edu
Cc: w3c-rdfcore-wg@w3.org

From: pat hayes <phayes@ai.uwf.edu>
Subject: Re: response to issue pfps-09
Date: Wed, 5 Feb 2003 17:15:53 -0600

> >From: pat hayes <phayes@ai.uwf.edu>
> >Subject: Re: response to issue pfps-09
> >Date: Wed, 5 Feb 2003 13:46:11 -0600
> >
> >>  >From: pat hayes <phayes@ai.uwf.edu>
> >>  >Subject: response to issue pfps-09
> >>  >Date: Tue, 4 Feb 2003 17:49:00 -0600
> >>  >
> >>  >>  I believe that there is a missing part of datatypes in the RDF model
> >>  >>  theory, and, moreover, that this missing part makes datatypes unusable
> >>  >>  in RDF.  The missing part is a mechanism for tieing a URI reference to
> >>  >>  a datatype.
> >>  >>
> >>  >>  ----
> >>  >>
> >>  >>  The MT assumes that datatypes are defined externally to RDF, and that
> >>  >>  part of this defining process involves associating a uriref with each
> >>  >>  datatype which can be used as its 'name', ie the semantic assumption
> >>  >>  is that the denotation is defined externally.
> >>  >
> >>  >The MT provides mechanisms for communicating the lexical space, value
> >>  >space, and L2V map of these externally defined datatypes to datatyped
> >>  >interpretations.  However, it is lacking a mechanism for communicating the
> >>  >RDF ``name'' of the datatype to datatyped interpretations.
> >>
> >>  I think there are two issues here that I (we?) have been getting confused.
> >>
> >>  1. A D-interpretation should require that the denotation of a
> >>  recognized datatype uriref is a particular datatype, as a semantic
> >>  condition.
> >>
> >>  2. Some *mechanism* should be provided in the semantics document for
> >>  assigning or attaching the denoted datatype to the datatype uriref.
> >
> >It appears to me that 2 is part of 1.  If a ``recognized datatype uriref is
> >a particular datatype'' then it is surely the case that that datatype must be
> >somehow assigned or attached to the datatype uriref.
> 
> Yes, somehow. But how, exactly, is not for the RDF WG to decide, seems to me.

Why not.  Without this, how can I use datatypes?

> Look, RDF assumes that urirefs denote, and that's all it assumes.  If 
> a uriref is being used to *name* something, ie if its denotation is 
> supposed to be fixed somehow and publicly accessible, then this 
> requires a process of baptism, of assigning a name to the thing 
> named. I do not know how to do that, and you are saying that neither 
> do you, and until there is such a process you don't know how to 
> baptize a new datatype. Indeed, I agree, I don't know either. But our 
> charter only requires us to incorporate the XML Schema datatypes, and 
> we have baptised those.
> 
> I think this larger problem - what are the appropriate protocols for 
> achieving baptism on the Web - is more than the RDF WG can tackle. It 
> is a larger and more comprehensive issue which impacts many other 
> things than RDF.

Well, why not just make RDF datatypes be four-tuples, instead of triples,
adding a URI reference?  A D-interpretation would then be required to
interpret the URI reference for datatypes as the datatype.  What is wrong
with this?

> [...]
> 
> >  >
> >>  Right, this was always the intention, that if ex:foo is a recognized
> >>  datatype uriref, then there is some datatype x such that in any
> >>  D-interpretation I , I(ex:foo) = x. I should make that more explicit,
> >>  clearly.
> >
> >But which URI reference denotes which datatype?
> 
> That is determined, presumably, by the agency which creates the 
> datatype and describes it in some standards document, or otherwise 
> publicises it. How is the meaning of any uriref determined? Im not 
> sure what kind of an answer you were expecting here.
> 
> >
> >What I want to be able to do in D-interpretations is
> >
> >1/ Create some datatypes, say octal and hexidecimal numbers.
> >2/ Be able to create typed literals that use these datatypes, for example
> >    "A"^^me:hexidecimal and "10"^^me:octal.
> >
> >I don't see how the current definition of D-interpretations gives me this
> >ability.
> 
> I don't think it does, indeed. All it is is a model-theoretic 
> semantics, not a universal datatype-defining system. In itself, it 
> doesn't give you the means to *create* anything, all it does is 
> define some semantic constraints to conform to.

Then D-interpretations are pretty much useless.

> >Without both of these, I don't see how RDF datatyping is useful.
> 
> Well, it lets you use the XML schema datatypes and it provides a 
> framework, or part of a framework, for future extensions. 

But then datatype extensions each have to be full-fledged semantic
extensions to RDF, instead of being just instantiations of the RDF
datatyping framework.

> It isn't a 
> complete comprehensive system for creating new datatypes on the Web. 
> I don't think there is any prospect of such a comprehensive system 
> being constructed at present, but there may be other initiatives 
> under way about which I know nothing, of course.
> 
> Pat

peter
Received on Wednesday, 5 February 2003 18:51:58 EST

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