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Reification -> Higher Order Logic question

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Mon, 27 Sep 2004 18:40:21 -0400 (EDT)
To: www-rdf-logic@w3.org
Message-ID: <Pine.LNX.4.44.0409271823100.19768-100000@tribal.metalab.unc.edu>

Apologies for introducing myself with what may be another obvious 
question, but at a recent XML conference I was at the one continual 
complaint was that "reification" seems to lead to misleading inferences 
and is generally hard to fit computationally within an implementation.

I thought about the problem briefly, and it appears that this is similar 
to the classic higher-order problem of logic, i.e. when one makes 
quantified predicates about predicates one leaves normal predicate logic and enters
higher-order logic. It appears that while higher-order logics are more 
expressive, but their properties make them more difficult, i.e. 
intractable and harder to make statements about, i.e. in  lower-order 
logic (My FOL->DL question revisited).  

Does anyone have a good logical story for how RDF reification replicates 
or has similar behavior? It would seem that this would be one method
to attempt to state useful things about RDF reified statements, even
if those inferences were not really DL.

Note the RDF Semantics states this problem clearly:  "Since an assertion 
of a reification of a triple does not implicitly assert the triple itself, this means that there are no 
entailment relationships which hold between a triple and a reification of 
it. Thus the reification vocabulary has no effective semantic constraints 
on it, other than those that apply to an rdf-interpretation.

A reification of a triple does not entail the triple, and is not entailed 
by it. (The reification only says that the triple token exists and what it 
is about, not that it is true. The second non-entailment is a consequence 
of the fact that asserting a triple does not automatically assert that any 
triple tokens exist in the universe being described by the triple. For 
example, the triple might be part of an ontology describing animals, which 
could be satisfied by an interpretation in which the universe contained 
only animals, and in which a reification of it was therefore false.)"

Ahhh....which I could see could lead to some non-intuitive reasoning
and difficulties with implementation. The named graph approach attempts
to solve this issue, correct?

				--harry

	Harry Halpin
	Informatics, University of Edinburgh 	
        http://www.ibiblio.org/hhalpin
Received on Monday, 27 September 2004 22:40:27 GMT

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