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Re: Datatype question

From: Geoff Chappell <geoff@sover.net>
Date: Mon, 24 Jun 2002 08:46:43 -0400
Message-ID: <053c01c21b7d$321564c0$825ec6d1@goat1>
To: "Patrick Stickler" <patrick.stickler@nokia.com>, "RDF Interest" <www-rdf-interest@w3.org>

Patrick,

Thanks for your response - a few comments inline below.

--geoff

----- Original Message -----
From: "Patrick Stickler" <patrick.stickler@nokia.com>
To: "ext Geoff Chappell" <geoff@sover.net>; "RDF Interest"
<www-rdf-interest@w3.org>
Sent: Monday, June 24, 2002 2:45 AM
Subject: Re: Datatype question


> On 2002-06-23 19:05, "ext Geoff Chappell" <geoff@sover.net> wrote:
>
> >
> > I'm sure this has come up in rdf core datatype discussions but I can't
find
> > in the archives why it was rejected. Can someone familiar with those
> > discussions clear this up for me?
> >
> > Why can't a datatype class be interpreted as a union of the datatype
values
> > and their string representations? and as a mapping from value to
> > representation when used as a property? for example:
> >
> > abbrev_integer the datatype contains the sets {10, 3} and {"10", "3"}
and
> > the mapping ("10"->10, "3"->3)
> > abbrev_integer the class contains the members {10, "10", 3, "3"}
> > abbrev_integer the property has extension (10, "10"), (3, "3")
> >
> > {range age abbrev_integer}
> > {age x "10"}
> >
> > is consistent with (and implies)
> >
> > {age x ?y}
> > {abbrev_integer ?y "10"}
> >
> > and is enough to indicate that ?y=10
> >
> > If a datatype is understood to contain a set of values, a set of
> > representations, and a mapping between the two sets, what is wrong with
just
> > defining that when viewed as a class, it looks like the union of the two
> > sets, when viewed as a property, it looks like the mapping (i.e.
different
> > aspects of the datatype are seen depending upon how it is used)?
> >
> > It seems so simple and fully captures the common usage of specifying a
value
> > by either it's string representation or in a more qualified form (using
the
> > same property).
> >
> > Thanks for any responses.
> >
> > Geoff Chappell
>
> Taking the class extension of a datatype to be the union of the lexical
> and value spaces was discussed back in February/March. C.f.
>
> http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0469.html
> http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Mar/0124.html
>
> Many members of the WG felt that this approach was "ugly" and
> it was ultimately rejected due to problems pointed out by
> Jos De Roo in
>
> http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Mar/0151.html
>

I see. I guess the effective disjunctive range (i.e. either a string or a
datatype value) makes this approach incompatible with owl:UniqueProperty. Of
course, you might be able to just say that it is just not correct to use
owl:UniqueProperty in the context of a datatyped property and define a
owl:UniqueDataTypeProperty, or... but I imagine that could be a slippery
slope that results in something truly ugly (like some of the solutions
proposed with six different variations and spelling of range :-)

> A functionally similar approach which also uses rdfs:range for
> expressing global datatyping constraints, which is one of two
> final proposals presently under consideration by the WG, is to
> have the literal node of the inline idiom simply denote
> the datatype value, where the literal node is similar to a blank node,
> but with the lexical form included as a contextually interpreted label.
>

I can see the value of the untidy literal approach to datatyping. I do think
though, there is a practical impementation advantage to tidy literals (which
admittedly may not outweight the cost of keeping them). It also seems that
the prohibition on literals as subjects pretty clearly indicates that the
current RDF design intends literals to be tidy.

[...]
> Cheers,
>
> Patrick
>
> --
>
> Patrick Stickler              Phone: +358 50 483 9453
> Senior Research Scientist     Fax:   +358 7180 35409
> Nokia Research Center         Email: patrick.stickler@nokia.com
>
>
>
Received on Monday, 24 June 2002 08:17:46 GMT

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