A Relational Model of Data for Large Shared Data Banks Future users of large data banks must be protected from having to know how the data is organized in the machine (the internal representation). A prompting service which supplies such information is not a satisfactory solution. Activities of users at terminals and most application programs should remain unaffected when the internal representation of data is changed and even when some aspects of the external representation are changed. Change in data representation will often be needed as a result of changes in query, update, and report traffic and natural growth in the types of stored information. Existing noninferential, formatted data systems provide users with tree-structured files or slightly more general network models of the data. In Section 1, inadequacies of these models are discussed. A model based on n-ary relations, a normal form for data base relations, and the concept of a universal form for data base relations, and the concept of a universal data sublanguage are introduced. In Section 2, certain operations on relations (other than logical inference) are discussed and applied to the problems of redundancy and consistency in the user's model. CACM June, 1970 Codd, E. F. data bank, data base, data structure, data organization, hierarchies of data, networks of data, relations, derivability, redundancy, consistency, composition, join, retrieval language, predicate calculus, security, data integrity 3.70 3.73 3.75 4.20 4.22 4.29 CA700609 JB February 13, 1978 10:57 AM 2046 4 2046 2710 4 2046 1515 5 2046 2046 5 2046 2046 5 2046 2046 5 2046 2155 5 2046 2406 5 2046 2710 5 2046 2715 5 2046 2716 5 2046 2717 5 2046 2718 5 2046 2765 5 2046 2817 5 2046 2888 5 2046 2901 5 2046 2957 5 2046 2959 5 2046 2965 5 2046 3087 5 2046 3154 5 2046 1389 6 2046 1515 6 2046 210 6 2046 1936 6 2046 1976 6 2046 1976 6 2046 1989 6 2046 378 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2046 6 2046 2060 6 2046 2110 6 2046 2406 6 2046 2451 6 2046 2451 6 2046 2452 6 2046 2715 6 2046 2715 6 2046 2715 6 2046 3133 6 2046 616 6 2046 616 6 2046 616 6 2046