The transformation of extended entity relationship generalisation hierarchies into tables and meta tables

Abstract

The transformation of generalisation hierarchies into relational format cannot be done in a natural way. The usual methods of implementing such a structure are either to compress the hierarchy into one table or to represent it by means of a separate table for each class and subclass in the hierarchy. However, both techniques are accompanied by specific problems which become unacceptable for hierarchies that are structurally unstable, have many subclasses and/or use specialising attributes applying to several of the subclasses. This paper proposes an alternative technique in which generalisation structures are mapped into collections of tables and meta tables, the latter containing data about the hierarchy. The entity relationship approach is chosen as a frame of reference.