A formal framework for ER schema transformation

Abstract

Several methodologies for semantic schema integration have been proposed in the literature, often using some variant of the ER model as the common data model. As part of these methodologies, various transformations have been defined that map between ER schemas which are in some sense equivalent. This paper gives a unifying formalisation of the ER schema transformation process and shows how some common schema transformations can be expressed within this single framework. Our formalism clearly identifies which transformations apply for any instance of the schema and which only for certain instances.