I'm not a big fan of OWL either. I think that you can get all the expressibility of OWL and more using rules - in fact the fastest current OWL reasoner, OwlIm,

I'm not a big fan of OWL either. I think that you can get all the expressibility of OWL and more using rules - in fact the fastest current OWL reasoner, OwlIm, is based on using rules to model owl. A constraint like this would be something like SELECT ?invalid WHERE { ?invalid rdf:Type your:Class . ?invalid your:value1 ?v1 . ?invalid your:value2 ?v2 . FILTER(?v1>?v2) } Sparql queries can contain a construct clause which turns them into rules. For querying an RDF view of a relational database, I don't think anyone has solved this yet - D2RQ tries but like you say the performance tends to suck. A lot of the current promising work is using triple stores to store RDF directly, with a big leader in Franz with Allegrograph.