Hi,
in UML you can always extend something (eg. association) with a stereotype. It is then something like a new type. In your case you might define a stereotype <<rdfDisjoint>> or so.
May be there is a standard RDF stereotype for this purpose. If so: Use it.
Stereotypes could be defined in UML profiles, just type them,.. and distributed them by MDG.
There is a e-book from Thomas Kilian about MDG. You find also a lot in the online help about stereotype, MDG,..
Regard,
Helmut