Database theory is now in a mature state, and this book addresses important extensions of the relational database model such as deductive, temporal and object-oriented databases. It provides an overview of database modelling with the Entity-Relationship (ER) model and the relational model providing the pivot on which the material revolves. The main body of the book focuses on the primary achievements of relational database theory, including query languages, integrity constraints, database design, comput able queries and concurrency control. The most important extensions of the relational model are covered in separate chapters. This book will be useful to third year computer science undergraduates and postgraduates studying database theory, and will also be of interest to researchers and database practitioners who would like to know more about the ideas underlying relational dat abase management systems and the problems that confront database researchers.