rdf_estimate_complexity(?Subject,
?Predicate, ?Object, -Complexity)Return the number of alternatives as indicated by the database internal
hashed indexing. This is a rough measure for the number of alternatives
we can expect for an rdf_has/3
call using the given three arguments. When called with three variables,
the total number of triples is returned. This estimate is used in query
optimisation. See also rdf_predicate_property/2
and
rdf_statistics/1 for
additional information to help optimizers.