- From: Boris Motik <boris.motik@comlab.ox.ac.uk>
- Date: Fri, 9 Nov 2007 11:15:04 -0000
- To: "'Giorgos Stoilos'" <gstoil@image.ece.ntua.gr>
- Cc: <public-owl-wg@w3.org>
You can't say this in the abstract syntax: the OWL 1.0 DL abstract syntax has been restricted to allow only for tree-like connections between individuals. With my examples I just wanted to make these two points: - We can't really give up on tree-like connections without sacrificing decidability of ontology entailment (which gives us a negative answer to ISSUE-46). - If we give up on "true" anonymous individuals altogether and treat them just as Skolem constants, then we can allow for arbitrary connections between individuals (which gives us a positive answer to ISSUE-46). In this case, we would, of course, need a way to state this in the OWL 1.1 Functional-Style Syntax. Such an extension, however, would be trivial. Boris > -----Original Message----- > From: public-owl-wg-request@w3.org [mailto:public-owl-wg-request@w3.org] On Behalf Of Giorgos Stoilos > Sent: 09 November 2007 11:08 > To: 'Boris Motik' > Cc: public-owl-wg@w3.org > Subject: RE: ISSUE-3: REPORTED: Lack of anonymous individuals > > > 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 11:15:55 UTC