ABSTRACT
This chapter examines how to improve the content and quality of entity-relationship diagrams for information modelling. It presents a dozen simple rules that, if followed, remove much of the inexactness and ambiguity which can creep into entity-relationship diagrams. These rules fall into three categories: Syntactic rules to encourage the correct use of entity-relationship diagram graphical figures, Semantic rules to encourage a meaningful diagram representation of the data being modeled, and Pragmatic rules to refine the diagram so it can be converted to a well-designed relational schema. Entity-relationship diagrams consist of graphical notations for describing conceptual schemas. A one-to-many relationship set between entity sets “A” and “B” implies that zero or one “A” entity can be related to zero, one, or more “B” entities. A many-to-many relationship set implies that any number of entities from each of two entity sets may participate in a single relationship. Syntactic rules describe how the graphical notation figures are combined to create an understandable diagram.
