> If bf:uri did not assert some degree of equivalence, then it shouldn't
> be a subproperty of bf:identifier
Let me begin by saying that if you understand bf:identifier as essentially meaning "equivalentResource" or "owl:sameAs" or something along those lines, then I totally understand your fear of someone using the same URI for the bf:Identifer /and/ the bf:Instance.
We've thought of the bf:identifier->bf:Identifier construct more as a way to record and capture details about an "identifier" itself more than a relationship that equates two like things. Our assumption presented another way: bf:Identifier represents an identifier, not the Thing the identifier identifies. (And that is why I've had a hard time seeing the potential identifier collision - to me they represent two distinct things.)