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Re: how a perl programmer might do datatypes in RDF

From: Dan Connolly <connolly@w3.org>
Date: Thu, 06 Dec 2001 17:26:09 -0600
Message-ID: <3C0FFE91.4DF717ED@w3.org>
To: Pat Hayes <phayes@ai.uwf.edu>, w3c-rdfcore-wg@w3.org
A couple clarifications...

Dan Connolly wrote:
> 
> Pat Hayes wrote:
> >
> [...]
> > >I understand the P/P++ proposal to actually muck
> > >with that level of interpretation; they actually
> > >allow model-theoretic interpretaions where the objects of
> > >       <rdfs:label>10</rdfs:label>
> > >and
> > >       <ex:shoeSize>10</ex:shoeSize>
> > >denote different things.
> > >
> > >The S/DC/PL proposals don't muck with things at that level.
> >
> > I'm not sure to what intuitions you are appealing when you use the
> > term 'muck with'.
> 
> I'm appealing to all the complications where, in order to
> figure out what the 10 in <rdfs:label>10</rdfs:label> denotes,
> you might have to get/trust other files, do inference,
> etc. to find a range for rdfs:label.
> 
> I'm appealing to the fact that simple RDF documents don't
> even entail themselves.

... don't even ential themselves in the P-style proposal.

> > Leaving aside the rhetoric, it is true that the
> > P-style proposals allow different occurrences of the same lexical
> > literal to denote different values. But isn't that exactly what XML
> > datatyping does,
> 
> No. XML datatyping has no notion of propositional content,
> model theory, entailment, or any of that sort of stuff.
> 
> And it certainly doesn't have the requirement that is
> so central to RDF: that the meaning of an RDF document,
> as a logical formula, is self-evident. To put it
> in black-and-white, testable terms: that every
> RDF document entails itself.
> 
> The XML Schema design accepts all the wishy-washiness where
> if you start with document X, depending on
> whether you choose to pair it with schema S1 or S2, the ...>10<...
> might denote an integer or a string.

... might be associated with the type integer or string.

The XML Schema spec doesn't speak of denotation.


> > and aren't we under a mandated requirement to
> > respect that?
> 
> No; we have mandate to make the datatypes in XML Schemas
> (date, integer, float, ...) available in the RDF world.
> 
> We don't have to mess up RDF's self-evident-ness to do it,
> as proposals S/P/DC show.
> 
> > More generally, isn't that what ANY datatyping scheme
> > does?
> 
> No, as perl and BCPL programmers know... and logicians, evidently...
> 
> > If all literals were unambiguous then there would be no need to
> > even use datatyping schemes. Traditional logical notations for
> > example have felt no need for datatyping schemes for exactly this
> > reason: they fix the meanings of things like numerals, and use other
> > syntactic constructions to denote things like character strings.
> 
> Bingo! Then we'll be in good company.
> 
> > If a
> > literal always denotes the same value, then there really is no
> > datatyping in the language at all, seems to me. I'm not averse to
> > that idea; it makes for a cleaner model theory , for one thing.
> 
> Amen.
> 
> >  But
> > I would like us to call a spade a spade, and if we decide to go with
> > one of the S/DC/PL proposals, to say loud and clear that we have
> > simply eliminated data-typing from RDF and do not plan to support XML
> > datatypes.
> 
> Datatyping was never in RDF, to my mind.
> But we certainly plan to support XML datatypes, in the same
> way that the logic folks support character strings
> built out of integers.
> 
> --
> Dan Connolly, W3C http://www.w3.org/People/Connolly/

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Thursday, 6 December 2001 18:26:11 EST

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