W3C home > Mailing lists > Public > www-rdf-logic@w3.org > July 2002

Re: Dataypes, literals, syntax

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 19 Jul 2002 17:47:07 -0400
To: phayes@ai.uwf.edu
Cc: jonathan@openhealth.org, www-rdf-logic@w3.org
Message-Id: <20020719174707W.pfps@research.bell-labs.com>

From: pat hayes <phayes@ai.uwf.edu>
Subject: Re: Dataypes, literals, syntax
Date: Fri, 19 Jul 2002 16:22:06 -0500

> >From: "Jonathan Borden" <jonathan@openhealth.org>
> >Subject: Dataypes, literals, syntax
> >Date: Fri, 19 Jul 2002 08:56:02 -0400
> >
> >>
> >>  I just noticed:
> >>  http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jul/0121.html
> >>
> >>  It got me thinking about literal datatypes (the above considers XML
> >>  datatypes).
> >>
> >>  Why not:
> >>
> >>  <rdf:Description rdf:about="foo://bar">
> >>      <ex:property xsi:type="xsd:integer">10</ex:property>
> >>  </rdf:Description>
> >>
> >>  being defined to parse to:
> >>
> >  > <foo://bar> ex:property xsd:integer"10" .
> >  >
> >>  wouldn't this solve much of the datatypes debate -- it would _syntactically_
> >>  distinguish typed literals, as Drew McDermott correctly points out is the
> >>  way to go, and would avoid issues related to nonmonotonicity related to
> >>  interpreting a triple based on a schema that may or may not be present.
> >
> >This has been proposed several times, by several people, including myself,
> >most recently in
> >   http://lists.w3.org/Archives/Public/www-rdf-comments/2002JulSep/0024.html
> >The RDF Core WG has, for some reason, chosen not to accept this in any
> >guise, even as part of a datatyping facility for RDF.
> 
> One reason is that (as far as I can see; correct me if Im wrong here) 
> this proposal does not allow non-datatyped literals.  That (very 
> strong) constraint seems unacceptable for RDF and would clash with 
> established usage. 

There is nothing in this approach that would *prevent* untyped literals.
Literals could be as above, i.e., typed, or just strings, i.e., untyped.

This approach could be teamed with a treatment of untyped literals as
denoting an element of an opaque type; it could be teamed with a treatment
of untyped literals as denoting strings; it could be teamed with a
treatment of untyped literals as syntactic constructs whose denotation is
underspecified and that can be further constrained by, for example, range
statements.  (The last treatment, of course, has its own problems, but they
are exactly the same as they would be without typed literals.)

> In a related criticism, it does not (again, please 
> correct) allow for 'remote' datatyping, where the association of a 
> datatype with a property range imposes a datatype interpretation on 
> uses of the property in other statements.

Agreed.  Typed literals are typed.  But so what?  If you want to have
undertyped literals then you can also, as shown above.

> As an example of a problematic inference, consider whether
> 
> <foo://bar> ex:property xsd:integer"10" .
> <foo://baz> ex:property xsd:octal"12" .
> 
> should or should not entail
> 
> <foo://bar> ex:property _:xxx .
> <foo://baz> ex:property _:xxx .
> 
> and how this could be detected by a reasoner.

Well, first of all xsd:octal is not an XML Schema datatype.  Ignoring that,
what is problematic about this example?  The model theory would say that
the denotation of xsd:integer"10" is the member of the XML value space that
is the result of the XML Schema datatype integer lexical-to-value mapping
of the string "10", i.e., the integer 10.  Similarly, the model theory
would say that the denotation of xsd:octal"12" is the member of the XML
value space that is the result of the XML Schema datatype octal
lexical-to-value mapping of the string "12", i.e., the integer 10.  This is
no different from how any of the proposals put forward by the RDF Core
Working Group would have do work.

> Pat

In sum, I don't see any downsides to having typed literals, only upsides.
It is the way XML (Schema) handles typing of literals;  it allows an escape
from some of the problems with XML Schema datatypes having to do with union
datatypes; it provides a clear and clean way of locally typing literals;
it avoids the extra blank node junk in the RDF Core Working Group current
treatment of local typing. 

peter

PS: If people are *really* interested in trying to have something like this
in RDF, I can polish up and update one of my previous proposals along this
line.  I may even have a up-to-date proposal lying around somewhere, but
I'm not going to put more work into it without some hope of having some
impact.
Received on Friday, 19 July 2002 17:47:26 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:52:42 GMT