- From: Mikael Nilsson <mikael@nilsson.name>
- Date: Mon, 11 Oct 2010 16:14:56 +0200
- To: public-lld@w3.org
Hi all! I'm in the middle of finalizing my thesis on metadata interoperability and harmonization, and I'm right now formulating a section on RDF and application profiles, so the discussion I saw here comes at an interesting time for me :-) The issue from my point of view with using OWL for defining RDF application profiles, is that APs define domain-specific structural constraints while OWL adds semantics to existing classes. I.e. if I produce an OWL-based AP saying that the cardinality of dc:title is exactly 1, for a specific class, and someone else produces an OWL-based AP saying that the cardinality is 2 for the same class, the result is a *contradiction*. This differs substantially from the case with application profiles, where the cardinality is not seen as part of the semantics of a class, but rather part of a set of restrictions, external to and independent of the class. Multiple incompatible application profiles are perfectly normal. Therefore, publishing an OWL ontology defining domain-specific semantics for certain classes or properties is just as bad practice as if someone produces an RDF Schema saying the range of dct:creator is myorg:Employee. This defines new semantics of dct:creator, something that is simply not true, and can cause involuntary contradictions. The other issue is the open world assumption that I saw Pete mention, i.e. the fact that if an OWL ontology specifies a cardinality of 2 for dc:title, and only one is found, this results in the generation of a new dc:title statement, not in non-validity of the record. Thus, we would need an alternative semantics for OWL to perform validation. But that's exactly it - the semantics is "alternative" and on its face, the semantics of the published OWL file is something else entirely. As a concrete example, if I serve an OWL file from my web server, using application/rdf+xml as suggested by the OWL specs [1], the interpretation will be as RDF triples using the RDF and OWL built-in semantics, thus resulting in the generation of new triples, potentially contradiction with other ontologies, and not in validation as expected. What *would* work is using application profile specific classes for each separate OWL-based AP, and only constraining them, but that might appear a bit cludgy. So, I'm a bit unsure regarding using non-standard semantics of OWL. I don't really see a clean solution at the moment. /Mikael [1] http://www.w3.org/TR/owl-ref/#MIMEType
Received on Monday, 11 October 2010 14:15:31 UTC