The history of database research over the past 30 years is one of exceptional productivity that has led to the database system becoming arguably the most impor tant development in the field of software engineering- The database is now the underlying framework of the information system, and has fundamentally changed the way many organizations operate. In particular, the developments in this tech nology over the last few years have produced systems that are more powerful and more intuitive to use. This has resulted in database systems becoming increasingly available to a wider variety of users. Unfortunately, the apparent simplicity of these systems has led to users creating databases and applications without the necessary knowledge to produce an effective and efficient system. And so the 'software crisis' or, as it is sometimes referred to, the 'software depression' continues.

The original stimulus for this book came from the authors' work in industry, providing consultancy on database design for new software systems or, as often as not, resolving inadequacies with existing systems. Added to this, the authors' move to academia brought similar problems from different users - students. The objec tives of this book, therefore, are to provide a textbook that introduces the theory behind databases as clearly as possible and, in particular, to provide a methodology for database design that can be used by both technical and non-technical readers.

The methodology presented in this book for relational Database Manage ment Systems (DBMSs) - the predominant system for business applications at present - has been tried and tested over the years in both industrial and academic environments. It consists of three main phases: conceptual, logical, and physical database design. The first phase starts with the production of a conceptual data model that is independent of all physical considerations. This model is then refined in the second phase into a logical data model by removing constructs that cannot be represented in relational systems. In the third phase, the logical data model is translated into a physical design for the target DBMS. The physical design phase considers the storage structures and access methods required for efficient access to the database on secondary storage.