|In my opinion, OWL 2 is a great improvement over OWL 1 since it incorporates several expressive means which are relevant for applications.
However, regarding datatypes the restriction to unary relations (facets) seems unnecessary since concrete domains with n-ary relations are state of the art in DL research, and they certainly are useful in practice, since they allow to express, eg, that a car is at least as heavy as its engine.
It would thus be great if datatype relations with a higher arity could be included in the final version.
To: Hladik, Jan <email@example.com>
Subject: [LC response] To Jan Hladik
Thank you for your comment
on the OWL 2 Web Ontology Language last call drafts.
You have noticed that, in the current specification of OWL 2, only *unary* datatype relatations (facets) are supported and that, in theory, this restriction is unnecessary. The syntax is defined, however, in such a way that it can be easily extended to datatype relatations (facets) of arity larger than one. It is possible that such an extension (to the syntax and the semantics) will be published later as a separate document; this will depend on the state of and experiences with implementations.
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