Normalisation

Abstract

In his seminal paper on the relational data model, E. F. Codd formulated a number of design principles for a relational database (Codd, 1970). These principles were originally formalised in terms of three normal forms: first normal form, second normal form and third normal form. The process of transforming a database design through these three normal forms is known as normalisation. By the mid-1970s third normal form was shown to have certain inadequacies and a stronger normal form, known as Boyce-Codd normal form, was introduced (Codd, 1974). Subsequently Fagin introduced fourth normal form and indeed fifth normal form (Fagin 1977, 1979). In this chapter we consider Codd 's original ideas on normalisation whilst also describing a graphic technique used for designing fully normalised schema. We particularly emphasise the use of normalisation as a bottom-up technique for database design.