Dear Jon, Suppose foaf:Person has as rdfs:comment something like "A class of http retrievable web documents, which contain information about persons" - If thats the case i can't see any problem to assert: There is a resource typed foaf:Person, which has format application/xhtml+xml If one accepts foaf:Person<--rdf:type-- ? --dc:format--> application/xhtml+xml as true and the only knowledge you have...Why the hack one could come to the idea, that ? would be, would have been or will be a person. Cheers, rs