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Re: Expressiveness of OWL

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Wed, 28 Apr 2004 20:02:02 +0100
Message-ID: <408FFFAA.5070605@hplb.hpl.hp.com>
To: Graham Klyne <gk@ninebynine.org>
Cc: www-rdf-logic@w3.org

Graham Klyne wrote:

> 
> I've been doing a bit more reading about Description Logics, and I come 
> to a conclusion that I haven't noted stated anywhere in the OWL 
> specifications...
> 
> (1) No "role composition" in OWL
> 
> The Description Logic literature makes mention of a "role constructor" 
> called 'compose'.  I find no equivalent property in OWL;  I don't think 
> this is surprising, as DL literature indicates that DLs containing 
> 'compose' are undecidable, but I'd like to be sure I'm not overlooking 
> anything.
> 

Correct - IIRC the DL literature shows that compose over functional 
properties is decidable (in the DL sense), but this is not support in OWL

Also excluded were unions and intersections of properties.

> (2) Limited expressiveness of OWL-based inferences
> 
> OWL expressiveness limited to FOL expressions with just monadic and 
> dyadic predicates and no more than two variables.  Assuming absence of 
> an equivalent to 'compose' in OWL, this result is noted in a couple of 
> places, most clearly among those I surveyed in [1].
> 
> What does this all mean?  Thinking in terms of Horn Clause rules:
>    A1,A2,...,An => B
> or
>    ~A1 \/ ~A2 \/ ... \/ ~An \/ B
> 
> (The results in [1] are based on conjunctive forms, but I am guessing 
> that this is a dual result that can be obtained by renormalization.)
> 
> This suggests that OWL-based inference can handle a maximum of two 
> variables between the antecedent and concequent of a rule, so something 
> like:
> 
>    :a :parentOf :b .
>    :b :parentOf :c .
> =>
>    :a :grandParentOf :c .
> 
> Is beyond the scope of an OWL based reasoner to infer.
> 
> Is this right, or am I missing something?
> 

that looks correct to me
> #g


Note procedurally what happened was not that these things were 
considered and rejected but that our charter said start with DAML+OIL, 
D+O did not have these things and noone suggested adding them.

Jeremy
Received on Wednesday, 28 April 2004 15:02:48 GMT

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