The definition of a relationship type includes its participant entity types and the cardinality constraints. Relationship
type refinement is the specification of additional constraints when some of the participant entities are also instances of
other entity types. The best known types of refinements are refinement of participants and refinement of cardinality constraints.
These refinements have been studied, up to now, only for conceptual models with single classification. In this paper we extend
previous work by dealing with conceptual models with multiple classification. We characterize the refinements in this context,
provide a graphical and textual notation for their specification, and give their formal definition in logical terms. Moreover,
we provide a set of necessary conditions to guarantee that a given set of refinements is valid.