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Re: What do the ontologists want

From: Graham Klyne <GK@ninebynine.org>
Date: Mon, 21 May 2001 13:25:04 +0100
Message-Id: <>
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?


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
Received on Monday, 21 May 2001 11:34:08 UTC

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