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SEM: All OWL reasoners will be incomplete?

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Wed, 4 Sep 2002 18:35:02 +0100
To: <www-webont-wg@w3.org>

I have just been reading one of the threads that went on while I was on

OWL semantics
and also the subthread
OWL semantics ( with focus on an axiomatization)

If I have understood Ian correctly
> Point 1b:
> It should NOT be possible to use OWL/RDF statements to constrain the
> meaning of OWL/RDF syntax. E.g., if myTransitive is a sub-class of
> transitiveProperty, then instances of myTransitive should NOT be
> treated by OWL as transitive properties. If we go down this road, then
> we need a (HOL) reasoner even to parse the syntax of an OWL ontology,
> to determine what is being said, and to check that it is valid OWL.
> It may even be IMPOSSIBLE to be sure that we
> have derived the complete syntactic meaning of an OWL ontology
> (because the language is undecidable).

The alternative being that sound and complete reasoners are too difficult to

However, the view that complete reasoning is possible in DL is based on a
restricted idea of what reasoning is (largely class subsumption reasoning,
and consistency checking)

So Ian brought up the case in



>This is wrong. The MT simply imposes a restriction that, in all
>models, the interpretation of a TransitiveProperty must be closed
>under transitivity. This does not mean that any property that is
>closed under transitivity in all models is necessarily a
>TransitiveProperty (such a situation could result from other causes,
>e.g., the properties interpretation being empty in all models, or the
>size of the domain being less than 3 in all models).

I find the entailments view of reasoning fairly compelling:
- an OWL document entails another if every interpretation of the first is
also an interpretation of the second.

A complete reasoner should be able to prove any valid entailment.

Thus, either it is the case that "any property that is closed under
transitivity in all models is necessarily a TransitiveProperty", or it is
the case that the concept owl:TransitiveProperty is in the domain of
discourse in an RDF style.

So, I am increasingly coming round to thinking that incompleteness is
inevitable ...

Received on Wednesday, 4 September 2002 13:35:13 UTC

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