An Note on a Categorical Semantics for ER-Models

Abstract

We have a look at the semantics of Entity-Relationship models, a popular device for modelling data, but lacking a stringent semantics. In an earlier paper we have shown how togenerate an algebraic specification for an extended ER-model; in this paper we extend the algebraic view of a model through a categorial interpretation. Inheritance induces a tree structure for an ER-model. This is decorated with objects from a suitable category, and we ask for a unifying view of this model. Our approach suggests using colimits as the semantics. It is shown that under very mild conditions the colimit exists, and that this colimit is an adjoint to the diagonal. Finally we show how tointegrate binary relations into this approach by studying two general conditions on the morphism associated to a relation.