Externalized and Internalized Notions of Behavioral Refinement

Many different behavioral refinement notions for algebraic specifications have been proposed in the literature but the relationship between the various concepts is still unclear. In this paper we provide a classification and a comparative study of behavioral refinements according to two directions, the externalized approach which uses an explicit behavioral abstraction operator that is applied to the specification to be implemented, and the internalized approach which uses a built-in behavioral semantics of specifications. We show that both concepts are equivalent under suitable conditions. The formal basis of our study is provided by the COL institution (constructor-based observational logic). Hence, as a side-effect of our study on internalized behavioral refinements, we introduce also a novel concept of behavioral refinement for