RE: Logic and Using The Semantic Web Toolbox

From: Ora.Lassila@nokia.com
Subject: RE: Logic and Using The Semantic Web Toolbox
Date: Tue, 12 Dec 2000 13:01:56 -0600

> Pat,
> 
> you wrote:
> > I was left with this impression after various conversations
> > with Stefan Decker and Dan Connelly, from reading the W3C
> > documents concerning RDF,  Tim Berners-Lee's writings, and
> > from subsequent discussion concerning the contraints on DAML
> > which arise from its having to be RDF-compliant, and from
> > reading various discussions by various people on the RDF
> > email archives.
> 
> Ah, but you should have read the RDF M+S spec :-)
> 
> Seriously, I believe that "semantic extensibility" means exactly that:
> *adding* some semantics. It seems that if we invent more stuff, we can do
> all kinds of things. I thought we were discussing what RDF was specificed to
> do/be.

I fear that parts of RDF are not suitable for this purpose.  In particular,
RDF already includes some ``semantic'' stuff, namely sets and reification,
that has a very shakey semantic status.  Sure, it is possible to produce
something at the next layer up that maps into RDF in some way.  But this
next layer will not be able to build on the shakey portions of RDF.

As an example, suppose I want to include sets in my version of the next
layer.  How am I to do this?  I have to make a whole bunch of choices about
how my sets will work (see below).  If I use the RDF syntax for sets, then
these choices will impact RDF sets.  In essence, I will be imposing my view
of sets onto RDF sets, which does not seem to be a valid way of extending
RDF.

I don't see how you can add semantics to constructs that already exist.  If
the constructs already exist, then they should have a meaning.  Semantic
extensibility should involve adding new constructs with their own meanings.

Peter Patel-Schneider


Some of the choices required for sets:

1/ Does the set membership relationship have to be well-founded?
2/ How are sets determined to be equal?
3/ Can sets be infinite?
4/ Can sets be partially specified?

Received on Tuesday, 12 December 2000 14:35:02 UTC