- From: Pat Hayes <phayes@ihmc.us>
- Date: Mon, 10 May 2004 10:56:32 -0500
- To: "Dimitrios A. Koutsomitropoulos" <kotsomit@hpclab.ceid.upatras.gr>
- Cc: www-rdf-logic@w3.org
>Hello, > >Can somebody explain some formal reason why the concrete and abstract >domains (i.e. the datatype and individual sets) have to be disjoint in OWL >DL? The rationale that was offered at the time was basically that datatypes can introduce arbitrarily complex conditions on class definitions, so that to allow datatyped values into a non-datatype class means that a (complete) reasoner might have to incorporate arbitrarily complex reasoning about domains defined by external means and this would infect the entire DL reasoning, with potentially disastrous effects on efficiency and even decideability. For example, allowing xsd:integer values into normal classes in effect adds arithmetic to the DL, since these values are required by the semantic conditions to be real, honest-to-God integers, and it is then possible to set up restrictions so that to determine class membership might require arbitrarily complex arithmetic calculations, eg the identity of two individuals might depend on whether a complex diophantine equation has one or two solutions. For a more prosaic example, the RDF built-in datatype rdf:XMLLiteral would require that every reasoner be able to deal with class reasoning over the domain of normalized XML documents, so that identity might depend on whether or not two XML documents normalized appropriately, eg if {a, b, XMLdoc1, XMLdoc2} has cardinality 3. By restricting datatypes to datatype classes, the problem is kept within manageable bounds and can often be farmed out to external reasoners specialized for each datatype, since datatype reasoning can be largely kept separate from reasoning about individuals. >Is there a description logic that drops this restriction? I do not know, but others might. I think that this is not really so much a DL-specific restriction as one which was imposed on what might be called general reasoner-engineering grounds. That is, one could make out a case for this style of restriction independently of the logical nature of the non-datatype part of the system. The SWRL proposal for example treats datatyping as a matter to be handled by 'built-ins', ie function calls to external evaluators, which is a similarly motivated separation of datatype value handling from (in this case) rule processing. Pat Hayes > > >Many thanks, > >Dimitrios A. Koutsomitropoulos > >Computer & Informatics Engineer >Postgraduate Researcher >High Performance Information Systems Laboratory > > Contact > e-mail: kotsomit@hpclab.ceid.upatras.gr > work: +30 2610 993805 > fax: +30 2610 997706 > http://www.hpclab.ceid.upatras.gr -- --------------------------------------------------------------------- IHMC (850)434 8903 or (650)494 3973 home 40 South Alcaniz St. (850)202 4416 office Pensacola (850)202 4440 fax FL 32501 (850)291 0667 cell phayes@ihmc.us http://www.ihmc.us/users/phayes
Received on Monday, 10 May 2004 11:56:34 UTC