The Relational Model

Abstract

In this chapter we describe the Relational Model. This was proposed by Codd, in 1970, long before any relational database system became commercially available. Consequently standards, such as the SQL language, have rapidly emerged in contrast to earlier database systems. The relational model consists of three components: a relation (this being the only data structure permissible in the model), the relational algebra and integrity rules. These are described in more detail in this chapter. The relational algebra is the basis on which the SQL retrieval language was developed. Two specific relational integrity rules were defined in the original model: entity integrity and referential integrity. Initially these integrity rules were not directly enforced by the Oracle RDBMS, but both types of integrity rules can be directly enforced in Oracle Version 7 Finally, in 1985 as RDBMS were becoming commercially available, E.F. Codd published his famous 12 `rules’ for determining whether a database management system can be called relational. Adherence to these rules was, at the time, an important weapon for individual RDBMS providers in the battle for market share.