The Relational Model
A relation is a mathematical term for a two-dimensional table such as the one shown in figure 3.15. It is characterised by rows and columns, each entry there being a data item value. The reason for calling this a relation rather than a matrix lies in the lack of homogeneity in its entries — the entries are homogeneous in the columns but not in the rows. A relational data base consists of such relations, which can be stored on a physical device in a variety of ways.
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- 1.D. L. Childs, Proc. IFIP Congress 1968 (North Holland) p. 162.Google Scholar
- R. E. Levein and M. E. Maron, Communs Ass. comput. Mach., 10 (1967) p. 715.Google Scholar
- 2.For brief descriptions of these systems, see C. J.Date, An Introduction To Data Base Systems (Addison-Wesley, New York, 1975) chapter 8.Google Scholar
- 3.E. F. Codd, Communs Ass. comput. Mach., 13 (1970) p. 377.Google Scholar
- 4.E. F. Codd, Normalised Data Base Structure: A Brief Tutorial, IBM Research RJ935, November 1971.Google Scholar
- 5.E. F. Codd, Further Normalisation of the Data Base Relational Model, IBM Research RJ909, August 1971.Google Scholar
- 7.E. F. Codd, Relational Completeness of Data Base Sublanguages, IBM Research RJ987, March 1972.Google Scholar
- 8.E. F. Codd, Recent Investigations in Relational Data Base Systems, IBM Research RJ1385, April 1974.Google Scholar
- 9.C. W. Bachman, quoted in Computer Weekly, April 8, 1976.Google Scholar