The Entity-Relationship Model Toward a Unified View of Data教程.pdfVIP

The Entity-Relationship Model-Toward a Unified View of Data PETER PIN-SHAN CHEN Massachusetts 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, infor- mation 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)