- From: Graham Klyne <GK@ninebynine.org>
- Date: Mon, 21 May 2001 13:25:04 +0100
- To: pat hayes <phayes@ai.uwf.edu>
- Cc: Sandro Hawke <sandro@w3.org>, www-rdf-logic@w3.org
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 11:34:08 UTC