Abstract
The relational model, or the ERD model, was introduced by Dr. Codd in the 70's and has evolved since the first draft which was written by him. The ERD (Entity Relationships Diagram) is a data model or a diagram for high level descriptions of conceptual models of data. It provides a graphic description to represent such data models in the form of diagrams containing the entities and the different associations (or relations) that we have between the elements. Such models are used in the upstream phases of the designing of computing systems. For example, they are used, for example, to describe the information that we need and/or the type of information which must be recorded in the databases during the phase of planning. In the case of the Merise method of the design of information system, the design is based on a database, and the conceptual model of data is, transformed into the logical model of data at a later stage. Like the relational model then, this model is changed into a physical model during the physical phase of design. Sometimes, these two last phases are called "physical design". A basic understanding of the relational model is necessary to effectively use relational database software such as Oracle, Microsoft SQL Server, or even personal database systems such as Access or Fox, which are based on the relational model.
