codd - Information Retrieval P BAXENDALE Editor A...

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Information Retrieval P. BAXENDALE, Editor 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 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] provide numerous references to work in this area. In contrast, the problems treated here are those of data independence-the independence of application programs and terminal activities from growth in data types and changes in data representation-and certain kinds of data inconsistency which are expected to become troublesome even in nondeductive systems. Volume 13 / Number 6 / June, 1970 The relational view (or model) of data described in Section 1 appears to be superior in several respects to the graph or network model [3,4] presently in vogue for non- inferential systems. It provides a means of describing data with its natural structure only-that is, without superim- posing any additional structure for machine representation purposes. Accordingly, it provides a basis for a high level data language which will yield maximal independence be- tween programs on the one hand and machine representa- tion and organization of data on the other. A further advantage of the relational view is that it forms a sound basis for treating derivability, redundancy, and consistency of relations-these are discussed in Section 2. The network model, on the other hand, has spawned a
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This note was uploaded on 01/09/2012 for the course CS CS273 taught by Professor Xifengyan during the Spring '11 term at UCSB.

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codd - Information Retrieval P BAXENDALE Editor A...

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