Modelo e-r

The Entity-Relationship Unified View of Data
PETER PIN-SHAN Massachusetts CHEN

Model-Toward

a

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 anddescription 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 toderive 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

Thelogical 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 achievedata 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 “red” may not be natural tosome people [25]. This paper presents the entity-relationship model, which has most of the advantages of the above three models. The entity-relationship model adopts the more natural view that the real world consists of entities and relationships. It
Copyright @ 1976, Association for Computing Machinery, Inc. General permission to republish, but not for profit; all or part of this material isgranted provided that ACM’s copyright notice is given and that reference is made to the publication, to its date of issue, and to the fact that reprinting privileges were granted by permission of the Association for Computing Machinery. A version of this paper was presented at the International Conference on Very Large Data Bases, Framingham, Mass., Sept. 22-24, 1975. Author’s address: Center forInformation System Research, Alfred P. Sloan School of Management, Massachusetts Institute of Technology, Cambridge, MA 02139.
ACM Transactions on Database Systems, Vol. 1, No. 1. March 1976, Pages 9-36.

10

-

P. P.-S. Chen

incorporates some of the important semantic information about the real world (other work in database semantics can be found in [l, 12, 15, 21, 23, and 29)). Themodel can achieve a high degree of data independence and is based on set theory and relation theory, The entity-relationship model can be used as a basis for a unified view of data. Most Ivork in the past has emphasized the difference between the network model and the relational model [22]. Recently, several attempts have been made to reduce the differences of the three data models [4, 19, 26, 30,311. This paper uses the entity-relationship model as a framework from which the three existing data models may be derived. The reader may view the entity-relationship model as a generalization or extension of existing models. This paper is organized into three parts (Sections 2-4). Section 2 introduces the entity-relationship model using a framework of multilevel views of data. Section 3 describes...