point for implementors with their own URI creation logic.
test for a fragment RDF::URI with base_uri constructor.
rename target as an object was pretty spotty to define.
implement Resource.reload to reset it, if required.
anything that fakes RDF::Queryable should work. More power in return for more difficult error messages.
supposed to be using the default repository
yielding the newly created instance, and calling #save! on them afterwards.