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

From: Giorgos Stoilos <gstoil@image.ece.ntua.gr>
Date: Fri, 9 Nov 2007 13:07:32 +0200
Message-Id: <200711091107.lA9B7WlJ027838@manolito.image.ece.ntua.gr>
To: "'Boris Motik'" <boris.motik@comlab.ox.ac.uk>
Cc: <public-owl-wg@w3.org>

Hi,

Indeed if you use triples syntax or FOL syntax (as you did initially) or any
other syntax that allows you to play with variable, then you can construct
these things/problems. But I was asking about using OWL abstract syntax.

Greetings,
-gstoil

> -----Original Message-----
> From: Boris Motik [mailto:boris.motik@comlab.ox.ac.uk]
> Sent: Friday, November 09, 2007 12:50 PM
> To: 'Giorgos Stoilos'
> Cc: public-owl-wg@w3.org
> Subject: RE: ISSUE-3: REPORTED: Lack of anonymous individuals
> 
> Hello,
> 
> You can use bnodes in RDF data arbitrarily. Take a look at
> 
> http://www.w3.org/TR/rdf-primer/#structuredproperties
> 
> There, you'll see triples containing identifies form _:xxx; all of these
> are bnodes. Each such identifier is taken to represent one
> existentially quantified variables.
> 
> 
> 
> The bnodes in RDF are the same as labelled nulls in databases. Database
> people have studied in depth what kind of semantics is
> appropriate for null values. A really good paper on this topic is the
> following:
> 
> Tomasz Imielinski, Witold Lipski Jr.: Incomplete Information in Relational
> Databases. J. ACM 31(4): 761-791 (1984)
> 
> The practical consequences, however, are rather severe: answering queries
> with labelled nulls is NP-complete. This is one of the
> main reasons why practical database systems don't implement labelled
> nulls. (Another reason is that your answers are not so much
> better even if you use labelled nulls.)
> 
> Boris
> 
> 
> > -----Original Message-----
> > From: Giorgos Stoilos [mailto:gstoil@image.ece.ntua.gr]
> > Sent: 09 November 2007 10:18
> > To: 'Boris Motik'
> > Cc: public-owl-wg@w3.org
> > Subject: RE: ISSUE-3: REPORTED: Lack of anonymous individuals
> >
> >
> >
> > > -----Original Message-----
> > > From: Boris Motik [mailto:boris.motik@comlab.ox.ac.uk]
> > > Sent: Thursday, November 08, 2007 2:14 PM
> > > To: gstoil@image.ece.ntua.gr; public-owl-wg@w3.org; 'Carsten Lutz'
> > > Subject: RE: ISSUE-3: REPORTED: Lack of anonymous individuals
> > >
> > > Hello,
> > >
> > > Here is an explanation how anonymous individuals in ABoxes correspond
> to
> > > conjunctive queries. I will use a "pidgin" LaTeX
> > > first-order logic notation for this. I'll use _:x for anonymous
> > > individuals, and I'll use != for inequality (DifferentFrom)
> > > assertions and & for conjunction.
> > >
> > >
> > > Imagine you have an ABox A containing the following assertions:
> > >
> > > (1)  hor(_:1,_:2)
> > > (2)  ver(_:2,_:3)
> > > (3)  ver(_:1,_:4)
> > > (4)  hor(_:4,_:5)
> > > (5)  _:3 != _:5
> > >
> > > Under the traditional semantics, anonymous individuals are actually
> > > existentially quantified variables. Hence, the ABox A is
> > > actually equivalent to the following first-order formula \varphi:
> >
> > Hello,
> >
> > But is it possible to have the above statements in OWL 1.1? Since _:3
> and
> > _:5 are anonymous how can you refer to them in this difference assertion
> > (!=)?
> >
> > Greetings,
> > -gstoil
Received on Friday, 9 November 2007 11:07:54 GMT

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