Entity Modelling

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The Entity Modelling Tutorial Part One — Entities, Relationships and Attributes

This chapter is a tutorial on the use of entity modelling notation.

Previously, in types of things, we introduced boxes as the diagrammatic representation of types of entities. In the sections which follow we describe the conventions for describing the properties of the differing types of entities and their inter-type relationships including relationship cardinality and optionality (the crows foot and dashing of lines), relationship disjunction (the exclusion arc), recursion (looping structures), type generalisation (nested boxes) and the representation of the absolute (diagram root). The notation is as used in the SSADM method as described, for example, in Richard Barker's book1, but with some refinements supported by additional notation and diagramming conventions including one that distinguishes and foregrounds composition relationships.

The basics of the notation are introduced in the early sections :

At this point we move into less traditional areas:

1 Barker, Richard. Case Method: Entity Relationship Modelling. Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA, 1990.