W3C home > Mailing lists > Public > www-rdf-logic@w3.org > May 2001

Re: What do the ontologists want

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Mon, 21 May 2001 11:58:03 -0400
To: GK@ninebynine.org
Cc: www-rdf-logic@w3.org
Message-Id: <20010521115803Y.pfps@research.bell-labs.com>
In defense of stripped-down RDF, there is nothing technically wrong with a
logical formalism that can represent only positive ground triples.  Such a
formalism can certainly convey some useful semantic information.

It is just that such a representation formalism cannot be used to
*represent* anything more than positive ground triples.  Using positive
ground triples to encode a more-expressive formalism requires encoding, which
requires a new semantics, defined on top of the semantics for the positive
ground triples, and makes it essentially impossible to use the semantics
for the positive ground triples to represent domain information.

Peter F. Patel-Schneider
Bell Labs Research 

From: Graham Klyne <GK@ninebynine.org>
Subject: Re: What do the ontologists want
Date: Mon, 21 May 2001 13:25:04 +0100

> I think this example+explanation is one of the clearer expositions of what 
> RDF can and cannot do.  I suspect that many proponents of RDF recognize 
> this without being very clear about how to articulate it.
> I don't think any of the long-term advocates of RDF expect it to be able to 
> express all meanings (or even any universal truths?) using only semantics 
> defined for core RDF.
> I think the interesting question is:  can the RDF core framework alone 
> convey *any* useful semantics, or is it no more than an abstract syntax 
> over which semantics must be defined?
> #g
> At 08:54 PM 5/18/01 -0500, pat hayes wrote:
> >>For an example, let me introduce a propositional logic and provide a
> >>rule R which says that given triple <a,b,c> anyone may infer triple
> >><d,e,f>.  This logic is not very expressive; it does not even allow
> >>conjunction in the premise:
> >>
> >>    <R, premise, RP>
> >>    <RP, subject, a>
> >>    <RP, predicate, b>
> >>    <RP, object, c>
> >>    <R, conclusion, RC>
> >>    <RC, subject, d>
> >>    <RC, predicate, e>
> >>    <RC, object, f>
> >>
> >>Each of these triples is true itself, while also building a structure
> >>for us.
> >
> >How does this convey the meaning that you indicate, ie that <d,e,f> can be 
> >inferred from <a,b,c> ? It simply says that some things exist called 'R', 
> >'RP' and 'RC', which stand in some undefined relationship to a, b, c, and 
> >so on. The RDF data model provides no further meaning, and the model 
> >theory for RDF provides no further meaning. So no inferences are sanctioned.
> >
> >If you want this kind of structure to actually mean somethingmore than 
> >this - in particular, if you want it to have the force of an implication, 
> >as indicated - then you need to state truth-conditions which support that 
> >larger meaning. But those truth-conditions will have to refer not more 
> >than  the RDF syntax; they depend on the particular relation symbols you 
> >have used: in this case, 'premis' and 'conclusion'.  (You will also need 
> >to relate <a,b,c> to the three triples with 'RP' in the subject, but I 
> >presume that this wil be done by reification, so I won't dwell on it.) In 
> >other words, you have now given those symbols a *logical* meaning: they 
> >have become part of the logical syntax. This isn't RDF any more: it is 
> >something else, implemented in RDF.
> ------------
> Graham Klyne
> GK@NineByNine.org
Received on Monday, 21 May 2001 11:58:48 UTC

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