Summary
[Contents] [Next Page] [Prev Page] [Up] [Index] [How to Search]

Chapter 2. Entity-Relationship modelling

2.10 - Summary

Modelling data is the first phase of the development of ADAMO applications. ADAMO uses an ER model by which the world is viewed as entities and relationships between them. Various types of relationships are permitted and identified by the cardinalities assigned to the two related ESets. Fundamental to this approach is that a pictorial representation of a model is readily available, thus aiding in the development, and that every ESet and its associated relationship information maps to a table. The concepts introduced in this chapter are:

Entity

An object that can be distinctly identified, e.g. a person, a car, a subroutine, a wire, an event.

Relationship

An association between an entity in one ESet and an entity in another ESet.

Entity-Relationship model

Originally proposed in 1976 by P. Chen. It models reality in terms of entities and relationships between them. Entities are described by their attributes and those having the same set of attributes are grouped into entity sets (ESets). The set of all relationships between the entities in two entity sets is known as the relationship set (RSet).

Cardinality

The range of the number of entities that an entity in an ESet can be related with respect to a relationship.

Subschema

A conveniently sized part of a complete ER model.

Table

The basic data structure of ADAMO. Each table contains all attribute and relationship data for all the entities in an ESet.

___________________________________________________________________________

BR and MR - CERN PTG - ADAMO Users Guide for Version 3.3 - 11 Oct 93