hasKey axioms allowed for the empty set of properties

Hi!

In the reverse RDF-Mapping of owl:hasKey, there is no constraint on the size of the argument list. This means that a key axiom may be defined for the empty set of properties. Also, it looks to me that the empty set is allowed in the Structural Specification (Functional Syntax), either. 

I don't think that empty key axioms are particularly useful, and I can see that they have peculiar semantic ramifications.

So I propose to require at least one property for key axioms in both the Structural Spec and the reverse RDF-Mapping.

Cheers,
Michael

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Dipl.-Inform. Michael Schneider
Research Scientist, Dept. Information Process Engineering (IPE)
Tel  : +49-721-9654-726
Fax  : +49-721-9654-727
Email: michael.schneider@fzi.de
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