:- rdf_meta(
        cardinality(r,r,-)).

cardinality(S, P, C) :-
           setof(O, rdf_has(S, P, O), Os),
           length(Os, C).
cardinality(S, P, C) :- 
           C = 0.
        
labels(S, C) :-
        cardinality(S, rdfs:label, C).