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Re: Predicates and Arcs vs Triples RE: use/mention and reification: rdf:predicate/subject/object

From: pat hayes <phayes@ai.uwf.edu>
Date: Tue, 29 May 2001 11:41:35 -0500
Message-Id: <v04210106b7397b7cab50@[205.160.76.203]>
To: Graham Klyne <GK@NineByNine.org>
Cc: www-rdf-logic@w3.org
>At 01:52 PM 5/27/01 -0400, Jonathan Borden wrote:
>>This argument is oft stated. And in the early days of software, similar
>>arguments were made regading the lack of ability of a high level language to
>>express anything beyond what is expressed in machine language.
>
>That is very different from the argument I am advancing.  I am 
>saying that triples are something in which the various "high level 
>languages" of resource description might be grounded, and (assuming 
>adequate semantics) through which the various forms of "high 
>language may" be related.

Let me home in on this. A problem, I think, with a lot of this 
discussion, is that words like 'grounded' and 'related' are used 
without being clearly defined. There is certainly one sense in which 
any notation can be 'grounded' in triples, or represented as triples, 
since any graph can be encoded as a collection of triples. OK, let us 
agree on that. And these structures can be used to encode all of the 
syntactic forms of  various "high-level" languages, which can be 
provided with suitable semantics, presumably. All of that is 
uncontroversial. The heat is generated when one tries to fit these 
together. The RDF model tries to attach the semantics directly at the 
triples level, which forces it to use reification as a kind of 
universal syntactic solvent.  That is what some of us find an 
unacceptable trade-off, as it uses a huge burden of semantic 
expressivity (KIF is probably the only formalism on the planet with a 
fully defined truth predicate, and even that has never been used in 
practice by anyone, as far as I know, and is likely to be eliminated 
from the new KIF standard) to purchase a tiny advantage in 
interoperability (the property that any set of triples is 
well-formed.) Also, we are pretty sure it is going to lead to 
problems later: it is notoriously easy to produce paradoxes if used 
casually, it renders any 'genuine' usage of reification semantically 
suspect, and so on.

>[...]
>> >
>> > I think their is a fair community investment in the triple form, and that
>> > it should not be discarded unless we are certain that it is fundamentally
>> > inadequate.
>>
>>I submit that the community investment is in _arcs and nodes_ not triples
>>per se.
>
>I view "arcs and nodes" (as in directed labelled graphs) and 
>"triples" as different presentations of what is fundamentally the 
>same syntax.

I would respectfully suggest that you might want to re-think this 
identification; or at least, that you distinguish *syntax* from 
*structure*. A single structure can encode a variety of different 
syntaxes, but the logical semantics needs to have the actual syntax 
to attach to, not its implementation structure.

Pat Hayes

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Received on Tuesday, 29 May 2001 12:41:42 UTC

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