By V. Y. Lum
Communications of the ACM,
November 1970,
Vol. 13 No. 11, Pages 660-665
10.1145/362790.362794
Comments
In this paper a file organization scheme designed to replace the use of the popular secondary index filing scheme (or inverted files on secondary key fields) is described. Through the use of redundancy and storing keys (or access numbers of the records) that satisfy different combinations of secondary index values in “buckets,” it is possible to retrieve all keys satisfying any input query derived from a subset of fields by a single access to an index file, although each bucket may be used for many combinations of values and a combination of buckets may be required for a given query.
The method which, in its degenerate case, becomes the conventional secondary index filing scheme works similarly but has the following advantages: (1) the elimination of multiple accesses in many cases; (2) the elimination of false drops; (3) the elimination of computer time to perform intersection of key sets each qualified for one secondary index field only; and (4) the avoidance of long strings of keys when an index field appearing in a query has very few possible values. Redundancy, in some cases, is the same as the secondary indexing method. In the general case, trade-off between the number of accesses for query and redundancy exists.
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