Re: Literals (Re: model theory for RDF/S)

From: "Thomas B. Passin" <tpassin@home.com>
Subject: Re: Literals (Re: model theory for RDF/S)
Date: Tue, 2 Oct 2001 16:37:17 -0400

> [Peter F. Patel-Schneider]
> 
> > From: Patrick.Stickler@nokia.com
> [...]
> 
> > Again.  If you require that DIFFERENT URIs denote DIFFERENT things you
> > cannot later turn around and allow any two different URIs to denote the
> > same thing.  You have already said that they denote different things, and
> > this would introduce a contradiction.
> >
> > > I'm not against such a URI equivalence mechanism, I just don't (at the
> > > moment) see it belonging at the fundamental RDF layer. Maybe it *does*
> > > belong there, but I'm not convinced.
> >
> > This has nothing to do with whether RDF has any mechanism for equivalence
> > or difference.  It has to do with whether anything built on top of RDF can
> > ever have a non-trivial theory of URI or literal equivalence.
> >
> 
> Let's not forget the inverse case.  Many people will want to use RDF
> ***without*** another layer on top, like DAML+OIL, and it must be usable for
> them too.  This supports the need for a good understanding of the
> (semantic?) level at which new extensions, etc., should be applied,
> otherwise things that properly belong in higher layer will get thrown into a
> lower, and the reverse.

Agreed.

> For example, the syntactic equivalence of two URIs can be determined
> according to the normalization rules for URIs, and clearly belongs in RDF.
> RDF is supposed to have a datatype system, so it's reasonable to expect it
> to be able to tell strings from integers, but you can't apply that to
> literals because they can't be the subject of statements (unless that rule
> gets changed).

Also agreed, but I sense that there are quite a number of people that are
not in favour of RDF having a datatype system.  

> So if I want to use RDF without a higher layer, I have to take all literals
> as is, just as labels, or do my own private processing on them.
> 
> To me, this is inconsistent with the idea that RDF can make statements about
> "anything".  Without a higher layer, I can't make a statment about the
> nature of a literal.  I'm also not sure I can tell the difference between a
> URI string used as a literal value, and one used as a Resource-indicating
> URI.
> 
> I suggest, then, that RDF is the right layer for resolving this particular
> issue (depending, of course, on how you end up fixing it).

Also agreed.  Further, the only reason that DAML+OIL has its own datatype
mechanism is that there is not one in RDF(S).

> Forgive me for thinking while I type, but things are slowly getting clearer
> for me!
> 
> Cheers,
> 
> Tom P

Peter F. Patel-Schneider

Received on Tuesday, 2 October 2001 17:07:32 UTC