- From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
- Date: Wed, 14 Aug 2002 14:17:39 -0400
- To: schreiber@swi.psy.uva.nl
- Cc: www-webont-wg@w3.org
We would like to summarise (our understanding of) the current situation with respect to OWL semantics ahead of tomorrow's discussion. There are two proto-proposals [1] [2] currently available for the semantics of OWL. These proposals differ in a number of areas, but we feel that the most significant difference is how certain entailments come out. In proposal [1] there are entailments like Entailment 1: John in the intersection of Student and Employee entails John in the intersection of Employee and Student This is the standard way of treating syntactic constructs like intersection, union, conjunction, and disjunction. Proposal [2] necessarily has weaker entailment, with the result that the above is no longer an entailment. Extending the approaches in the two proposals to the logic layer would result in Proposal [1] supporting and Proposal [2] not supporting Entailment 2: `it is raining' or `today is Tuesday' entails `today is Tuesday' or `it is raining' We feel that any formalism that does not support entailments like 1 and 2 would manifestly fail to promote interoperability and to support the development of "applications that depend on an understanding of logical content" [3]. The two proposals differ on these entailments because Proposal [2] includes syntax in its domain of discourse. When syntax is in the domain of discourse the above entailments require comprehension principles which lead to paradoxes when the formalism has sufficient expressive power. OWL has sufficient expressive power for this purpose, e.g., see [4]. There are other differences between the two proposals, which are summarized below: Proposal [2]: - start with RDF - all RDF graphs are OWL KBs - OWL model theory is an augmentation of RDF model theory - everything is in the uniform domain of discourse - including syntax, so entailment is weak to avoid paradoxes - including classes, so classes are also instances Proposal [1]: - start with abstract syntax - only RDF graphs that correspond to the abstract syntax are OWL KBs - provide model theory for abstract syntax - entailment is standard - translate abstract syntax to RDF graphs - only RDF graphs that are the result of this translation are OWL KBs - Pat Hayes is providing an RDF-like model theory for those RDF graphs that correspond to the abstract syntax - translating the model theory into one based on triples - adding necessary syntactic constraints and "darkening" Ian Horrocks Peter F. Patel-Schneider [1] http://lists.w3.org/Archives/Public/www-webont-wg/2002Jun/att-0082/01-semantics.html [2] http://lists.w3.org/Archives/Public/www-webont-wg/2002Jun/0208.html [3] http://www.w3.org/2001/sw/WebOnt/charter [4] http://lists.w3.org/Archives/Public/www-webont-wg/2002Jan/0099.html
Received on Wednesday, 14 August 2002 14:17:49 UTC