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

[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.

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).

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).

Forgive me for thinking while I type, but things are slowly getting clearer
for me!

Cheers,

Tom P

Received on Tuesday, 2 October 2001 16:32:30 UTC