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Re: ISSUE-79 (EL++): REPORTED: EL++ Variants

From: Bernardo Cuenca Grau <bcg@cs.man.ac.uk>
Date: Wed, 28 Nov 2007 18:56:50 +0000
Message-ID: <474DB9F2.5020206@cs.man.ac.uk>
To: OWL Working Group WG <public-owl-wg@w3.org>

The variant of EL++ included in the Tractable fragments Document is 
based on the one in the 2005 IJCAI paper by Carsten and others:

http://lat.inf.tu-dresden.de/~clu/papers/archive/ijcai05.pdf

At the time of writing, however, I also included domain and range axioms 
in the description of the fragment. Obviously domain  axioms are 
directly expressible in EL++, as described in the paper above, but this 
is not the case with range axioms. At the time of writing, I had some 
informal discussions with people, including the people in Dresden and my 
understanding was that range axioms, even if not directly expressible 
could be easily added and handled while preserving the nice properties 
of EL++.
It seems from what Carsten says that this is not the case and therefore 
the variant of EL++ in the tractable fragments document  seems to be broken.

I have a question, however, concerning the  interaction between range 
restrictions and role inclusion axioms. Note that the EL++ version in 
the fragments document does impose some restrictions in the use of 
(complex) role inclusion axioms, namely the same ones as SROIQ imposes. 
My question is whether these restrictions are not sufficient.  If they 
do not suffice, I agree with Carsten in that identifying a variant of 
EL++ that allows for domain and range and imposes reasonable constraints 
in the use of role inclusion axioms would be  a good thing to have and 
that version should be the one included in the document.

I think that the issue whether this fragment which should be called 
``OWL Light" is a much more controversial one. In principle I think 
there should be no single ``OWL Light'', but a reasonable menu of 
choices for such an OWL Light that each particular user could pick 
depending on his application needs.

Bernardo



OWL Working Group Issue Tracker wrote:
> ISSUE-79 (EL++): REPORTED: EL++ Variants
>
> http://www.w3.org/2007/OWL/tracker/issues/
>
> Raised by: Bijan Parsia
> On product: 
>
> (On behalf of Carsten Lutz.)
>
> There are at least two versions of EL++ that are tractable. These
> two versions are incomparable in expressive power, and the current
> document lists only one of them. The fragment that is not listed
> offers both domain and range restrictions and captures, for example,
> the ontology NCI. What it does not have is role inclusions.
>
> An obvious remedy would be to list both fragments of EL++. However, I
> have hope that we can do better. We might be able to give a fragment
> that (unlike the one listed at the moment) truely resides inside OWL
> 1.1, that has domain and range restrictions, and that has (acyclic)
> role inclusions and is still tractable. *This* is actually the
> fragment that I think should be OWL Light (see ISSUE-78 on
> tractable fragments).  I need some time to work out details.
>
>
>
>
>   
Received on Wednesday, 28 November 2007 19:01:50 GMT

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