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RE: ISSUE-3: REPORTED: Lack of anonymous individuals

From: Boris Motik <boris.motik@comlab.ox.ac.uk>
Date: Tue, 27 Nov 2007 19:56:40 -0000
To: "'Web Ontology Language \(OWL\) Working Group WG'" <public-owl-wg@w3.org>
Message-ID: <005f01c8312f$a0940be0$2711a8c0@wolf>


Regarding anonymous individuals, I would just like to point out that one of the design goals of OWL 1.1 DL was to clean up the
specification and bring it closer to what OWL DL users and implementors are dealing with in practice. (Please note that I refer here
to OWL 1.1 DL, not to OWL 1.1 Full.)

- *All* currently implemented reasoners treat anonymous individuals as Skolem constants.

- The users of OWL 1.1 DL never ask queries containing ABoxes that contain anonymous individuals. If some form of querying is
required, people use some explicit query language.

- No OWL DL parser (to my knowledge at least) actually checks whether the anonymous individuals are really tree-like or not.

Thus, the OWL 1.0 DL specification contains some conditions that are not taken into account in the implemented systems and tools.
Therefore, I am just not sure whether bringing this legacy into OWL 1.1 DL is really necessary. The OWL 1.1 DL specification is
bound to be quite complex, and making it more complex by adding some practically irrelevant conditions will not improve it.

Therefore, a viable option might really be to either

- drop anonymous individuals explicitly in OWL 1.1 DL (and perhaps say in some note that such individuals can be dealt with for all
practical intents and purposes by Skolemization), or

- allow for arbitrary individuals in the ABox, but treat them as Skolem constants.

Regardless of which of these two solutions we pick, we are going to get much closer to what the implementations are supporting and
what the users really need. Thus, such a solution is bound to be of higher practical value than adding some complex restriction on
anonymous individuals being necessarily tree-like. In a way, this justifies the reason for developing OWL 1.1 DL in the first place.
Technically speaking, such a specification would be backwards incompatible; however, practically speaking, nobody will care, so this
is at best an academic issue.



> -----Original Message-----
> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org] On Behalf Of Jeremy Carroll
> Sent: 27 November 2007 11:25
> To: Ivan Herman
> Cc: Alan Ruttenberg; Boris Motik; 'Web Ontology Language (OWL) Working Group WG'
> Subject: Re: ISSUE-3: REPORTED: Lack of anonymous individuals
> I am surprised we haven't yet opened this issue, and closed it.
> Early discussion seemed to indicate potential agreement between me and
> Boris who seem to be at extremes, and so that agreement could well be
> one which would hold consensus.
> e.g.
> see
> http://lists.w3.org/Archives/Public/public-owl-wg/2007Nov/0218
> I guess I hope we can dispose of this one soon (and the related ISSUE-46)
> Jeremy
Received on Tuesday, 27 November 2007 19:57:27 UTC

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