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[SWC] Re: [OWL Compatibility] Re: RIF & OWL compatibility

From: Jos de Bruijn <jos.debruijn@deri.org>
Date: Thu, 12 Jan 2006 11:46:14 +0100
To: Enrico Franconi <franconi@inf.unibz.it>
Cc: public-rif-wg@w3.org
Message-Id: <1137062774.8809.19.camel@localhost.localdomain>
On Sun, 2006-01-08 at 21:39 +0100, Enrico Franconi wrote:
> On 4 Jan 2006, at 08:59, Jos de Bruijn wrote:
> >> What is a "superset approach"? Is it really true that "There are
> >> several nonmonotonic logics which are candidates for such a
> >> formalism, such as circumscription, autoepistemic logic and default
> >> logic"? Can you encode DL's in such logics? Well, yes - if you really
> >> mean a superset of FOL with non-mon operators; but does it really
> >> make sense to say that? In the "black box approach", as you mean it,
> >
> > Yes, a superset of FOL was meant here. This approach probably doesn't
> > make sense in a practical setting, but it is a possible approach.
> 
> I am not really sure that such a superset of FOL (capturing both the  
> LP aspects and the DL aspects) exists and/or has been studied.  
> Although we can not exclude that such a beast exists, it has unknown  
> properties and therefore I would not even mention this possibility.

I am also not promoting this approach. My intention was to point out
this possibility and then conclude that this is not in the scope of this
WG.

> 
> >> it is *not* true that "OWL DL and the LP rules are viewed as black
> >> boxes which exchange only ground facts". Please, first study Rosati's
> >> and Eiter's works before stating these things. Moreover, the
> >> statement: "Second, the existential consequences cannot be reused,
> >> since it is not possible to deal with existential information in LP
> >> rules", is false.
> >
> > I actually defined the black box approach there, and I defined that  
> > the
> > OWL DL ontology and the LP rule base are viewed as black boxes which
> > exchange ground fact. Perhaps this approach needs to be refined,  
> > but I'm
> > not sure.
> > I'm not yet aware of Rosati's approach, but his paper is on my stack.
> > As far as I understood Eiter et al's approach, it works exactly as
> > described here. One can include queries to a DL ontology in the  
> > body of
> > LP rules; it is also possible to specify which facts needs to be added
> > to the DL ontology before executing the query.
> 
> Things are more complex than this, and several different incompatible  
> options are available. First of all, you are neglecting all the FOL- 
> based approaches (e.g., SWRL, Carin, etc). If we stay in what you  
> call LP semantics for rules, then the interaction between rules and  
> the ontology would be better characterised by looking at how the  
> models of the rules and the models of the ontology do interact,  
> rather that by having ground facts exchanges.

Agreed.

> > Wrt. the existential information: the semantics of LP rules is  
> > based on
> > Herbrand models, which means (among other things) that every  
> > individual
> > in the universe is represented with a name in the language. This makes
> > it impossible to truly capture existential information.
> 
> I disagree. For example, In Rosati's approach non-distinguished  
> varibales (i.e., existentials) are not restricted to the herbrand  
> universe. BTW all the use cases in Managing Incomplete Information  
> <http://www.w3.org/2005/rules/wg/wiki/ 
> Managing_incomplete_information> would be correctly handled by  
> Rosati's approach.

Rosati uses the standard names assumption, which excludes considering
unnamed individuals, thus, certain kinds of existential knowledge cannot
be captured in his approach.

If you have a name for the individual, then you can certainly deal with
it in the logic program.
However, if we would take the following example:

take the following first-order sentence:
\exists x. p(x)

and the following rule:

r <- p(x)

One cannot conclude r, because there is no name a such that p(a).


Best, Jos


--
Jos de Bruijn,        http://www.debruijn.net/
+43 512 507 6475         jos.debruijn@deri.org

DERI                      http://www.deri.org/
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Received on Thursday, 12 January 2006 10:45:58 GMT

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