Information Retrieval

Information Retrieval

A Relational Model of Data for

Large Shared Data Banks

E. F. CODD

IBM Research Laboratory, San Jose, California

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. Changes 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

data sublanguage are introduced. In Section 2, certain opera-

tions on relations (other than logical inference) are discussed

and applied to the problems of redundancy and consistency

in the user’s model.

KEY WORDS AND PHRASES: 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

CR CATEGORIES: 3.70, 3.73, 3.75, 4.20, 4.22, 4.29

1. Relational Model and Normal Form

1 .I. INTR~xJ~TI~N

This paper is concerned with the application of ele-

mentary relation theory to systems which provide shared

access to large banks of formatted data. Except for a paper

by Childs [l], the principal application of relations to data

systems has been to deductive question-answering systems.

Levein and Maron [2] pr

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