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From: Giorgos Stoilos <gstoil@image.ece.ntua.gr>
Date: Wed, 28 Nov 2007 21:06:18 +0200
Message-Id: <200711281906.lASJ6Iao011321@manolito.image.ece.ntua.gr>
To: "'Bernardo Cuenca Grau'" <bcg@cs.man.ac.uk>
Cc: "'OWL Working Group WG'" <public-owl-wg@w3.org>

Hi Bernardo,

The motivation for choosing DL-Lite_R seems quite reasonable.

On the other hand personally (if there is going to be only one DL-Lite
selected at the end of the day) I would prefer DL-Lite_F for the following
three reasons:

i) DL-Lite_R has not been (AFAIK) explicitly defined in the literature. What
has been defined is DL-Lite_(R, conjunction) which also includes existential
quantification over atomic concepts (some R.A).

ii) A DL-Lite_R algorithm has (again AFAIK) also not been explicitly
presented in the literature, but it is more-or-less left as an exercise to
the reader.

iii) Finally, I am not aware of any available implementation of DL-Lite_R. 

On the other hand DL-Lite_F does support the complements of i)-iii) above.


> -----Original Message-----
> From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org]
> On Behalf Of Bernardo Cuenca Grau
> Sent: Wednesday, November 28, 2007 7:58 PM
> To: OWL Working Group WG
> Subject: Re: ISSUE-80 (DL-Lite): REPORTED: DL-Lite
> Ok. I see quite a lot of discussion concerning the tractable fragments
> document, and I will try to reply to all the issues.
> The selected version of DL-Lite is DL-Lite_R. As Carsten points out,
> there are other variants of DL-Lite for which reasoning is tractable.
> These variants share a common core, but provide different extensions to
> this core corresponding to different choices that one has to make in
> order to keep tractability. For example, DL-Lite_R extendes the ``core''
> of the language with role inclusion axioms. DL-Lite_F extends it with
> role functionality of roles and their inverses. If both role
> functionality and role inclusion axioms were to be included, the nice
> computational properties of the DL-Lite family of languages would be
> compromised.
> The selection of DL-Lite_R was motivated by the fact that it is a proper
> extension of the DL subset of RDF-Schema, which provides role-inclusion
> axioms but not functionality, and therefore DL-Lite_R is a language that
> lies in between such DL subset of RDF-Schema and OWL Lite.
> In any case, I agree that these choices should be discussed and that we
> could do a better job in presenting all (or most of) the variants. Also,
> as Carsten points out, there is also a distinction between tractability
> of reasoning and the fact that query answering can be handled using
> RDBMS, and this should probably be made explicit if we are to present
> other variants of DL-Lite.
> I think we should discuss the alternatives within the WG
> Bernardo
> OWL Working Group Issue Tracker wrote:
> > ISSUE-80 (DL-Lite): REPORTED: DL-Lite
> >
> > http://www.w3.org/2007/OWL/tracker/issues/
> >
> > Raised by: Bijan Parsia
> > On product:
> >
> > (On behalf of Carsten Lutz.)
> >
> > There are many versions of DL-Lite around, all of them tractable,
> > and many (but not all) of them reducible to query answering in
> > RDBMS. I wonder how the fragment of DL-Lite was selected that is
> > currently in the document and what are the alternatives? Maybe
> > Bernardo can comment on this.
> >
> >
> >
> >
> >
Received on Wednesday, 28 November 2007 19:07:06 UTC

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