 of the sum logic,
and we use the instance aspect to specify an appropriate subset of the
instances (entity, function and relation) of the sum logic. This logic
invariant induces a quotient logic over the sum logic: types are the
quotient classes of the corresponding equivalence relation, whereas
instances called instance connections are pairs of instances, one from
each participant ontology, that are indistinguishable vis-&agrave;-vis
the mediating ontology. This quotient logic represents a virtual
ontolog