Standard transformations for the normalization of ER schemata

摘要

Normalization, which makes up the core of the design theory for relational databases, is also considered an important technique to improve the quality of ER schemata. For ER schemata, however, local normalization based on standard transformations is better suited than a global approach similar to that used by relational normalization algorithms. We first present a framework for describing ER schema transformations. Then a normal form, ER-BCNF, is defined which corresponds to BCNF, and a complete set of transformations to achieve this normal form is suggested. The question how null values should be dealt with is raised afterwards. Finally, we discuss how the theory may be applied and give an outlook on future research.