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Re: Two bugs in the OWL 2 Direct Semantics and the SS&FSS documents

From: Boris Motik <boris.motik@comlab.ox.ac.uk>
Date: Mon, 29 Mar 2010 22:23:28 +0100
Cc: public-owl-comments@w3.org
Message-Id: <EF231DC5-F4AF-4E9D-BF6C-A7EAAAD30750@comlab.ox.ac.uk>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
Hello,

The change would mean that no ontology can enforce ISNAMED to be true only on named individuals. This *does not* mean that an ontology can entail ISNAMED to be true of an anonymous individuals. Rather, this merely means that, if asked for an anonymous individual, ISNAMED can be concluded to be neither true nor false.

This, however, is just a technicality. If you don't check entailment of keys, you actually can't ask a question by means of which you would be able to tell the difference. Thus, for most practical intents and purposes, this change would be harmless.

Regards,

Boris

On 29 Mar 2010, at 22:10, Alan Ruttenberg wrote:

> On Mon, Mar 29, 2010 at 11:20 AM, Boris Motik
> <boris.motik@comlab.ox.ac.uk> wrote:
>> 
>> 1. A bug in the OWL 2 Direct Semantics
>> 
>> Section 2.3 of the Direct Semantics document defines the ISNAMED function, which is used in the definition of the semantics of easy keys. Unfortunately, this function has been defined to be true for an element of the domain *if and only if* it interprets a named individual, whereas it should be true *if* an element interprets a named individual (leaving open whether ISNAMED is true for other elements). This makes easy keys not so easy: as a side-effect of this definition, ISNAMED acts as a nominal, which has consequences for the computational properties of the profiles. In particular, ontology entailment (which is the basic computational problem for OWL 2) becomes NP-hard with keys in OWL 2 EL.
>> 
>> We can fix the error by the following two steps:
>> - We need to make ISNAMED a part of an interpretation. Thus, an interpretation needs to become a tuple of the form I = ( ΔI , ΔD , ⋅ C , ⋅ OP , ⋅ DP , ⋅ I , ⋅ DT , ⋅ LT , ⋅ FA , ISNAMED).
>> - We need to weaken the definition of ISNAMED from iff to if. That is, for each named individual a, ISNAMED(a^I) must be true (but not the other way around).
> 
> 
> Wouldn't that mean that there could be a valid OWL ontology where
> isNamed is true of an anonymous individual?
> 
> How would such an ontology be expressed in the functional syntax?
> 
> -Alan
Received on Monday, 29 March 2010 21:23:57 GMT

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