Representing extended entity-relationship structures in relational databases: a modular approach

A common approach to database design is to describe the structures and constraints of the database application in terms of a semantic data model, and then represent the resulting schema using the data model of a commercial database management system. Often, in practice, Extended Entity-Relationship (EER) schemas are translated into equivalent relational schemas. This translation involves different aspects: representing the EER schema using relational constructs, assigning names to relational attributes, normalization, and merging relations. Considering these aspects together, as is usually done in the design methodologies proposed in the literature, is confusing and leads to inaccurate results. We propose to treat separately these aspects and split the translation into four stages (modules) corresponding to the four aspects mentioned above. We define criteria for both evaluating the correctness of and characterizing the relationship between alternative relational representations of EER schemas.