The Entity-Relationship Model-Toward a Unified View of Data

The Entity-Relationship

Unified View of Data

PETER PIN-SHAN

Massachusetts

Model-Toward

a

CHEN

Institute of Technology

A data model, called the entity-relationship model, is proposed. This model incorporates some of

the important semantic information about the real world. A special diagrammatic technique is

introduced as a tool for database design. An example of database design and description using

the model and the diagrammatic technique is given. Some implications for data integrity, information retrieval, and data manipulation are discussed.

The entity-relationship model can be used as a basis for unification of different views of data:

t,he network model, the relational model, and the entity set model. Semantic ambiguities in these

models are analyzed. Possible ways to derive their views of data from the entity-relationship

model are presented.

Key Words and Phrases: database design, logical view of data, semantics of data, data models,

entity-relationship model, relational model, Data Base Task Group, network model, entity set

model, data definition and manipulation, data integrity and consistency

CR Categories: 3.50, 3.70, 4.33, 4.34

1. INTRODUCTION

The logical view of data has been an important issue in recent years. Three major

data models have been proposed: the network model [2, 3, 71, the relational model

[S), and the entity set model [25]. These models have their own strengths and

weaknesses. The network model provides a more natural view of data by separating

entities and relationships (to a certain extent), but its capability to achieve data

independence has been challenged [S]. The relational model is based on relational

theory and can achieve a high degree of data independence, but it may lose some

important semantic information about the real world [12, 15, 231. The entity set

model, which is based on set theory, also achieves a high degree of data independence, but its viewing of values such as “3” or...