A Primer on Relational Data Base Concepts

concepts cfrelational data base management systems are described. Characteristics of the relational approach are identi-jied and compared with present implementations of hierarchical and network data base systems. Depending on the application, a user may experience one or more of the following benejits of rela-tional systems described in this paper: ease of understanding, increased data independence, ease of use, sound theoretical basis, and generalized data dejinition. Types of applications most suited to hierarchical and network data base systems are ulso compared and contrasted. For about a decade there has been continuously increasing interest in relational data base systems, most of it initially created by university and research activities. A series of papers published by E. F. Codd in the early seventies are often cited as the earliest works on the subject.' Relational data base systems are now becoming available for operational data processing installations. Examples of such systems by IBM are Query-By-E~ample~'~ and IMPS.4 In addition, many research prototype systems have been implemented, as exemplified by System R5 and IS/1-PRTV.6'7 A number of other rela-tional systems are expected to become commercially available within the next few years.' " This paper describes basic concepts of relational data base systems and identifies potential benefits of the relational data base approach, comparing it with present implementations of hierarchic and network data base systems. What is a relational data base system? The most fundamental property of a relational data base system is that data are presented to the user as tables instead of networks or hierarchies. Thus, the data are structured in the form of tables Copyright 1981 by International Business Machines Corporation. Copying is permitted without payment of royalty provided that (I) each reproduction is done without alteration and (2) the J o u r n d reference and IBM copyright notice are included on the first page. The title and abstract may be used without further permission in computer-based and other information-service systems. Permission