Question about datatype property constraint.

Holger,

The current semantics for appear to assume that the domain of the SPARQL datatype function is RDF Term.  To the best I can determine, however, SPARQL doesn't specify the behavior for the datatype function when  applied to a non-literal.  The implementation that I tried returned "", but I suspect that a strictly conforming SPARQL implementation would probably treat this as a runtime error.  Do we need to add a bit to the semantics of this function to explicitly say what should happen in case of a non-literal object?

Harold Solbrig