Trees as data and file structures

Abstract

Trees have been important data structures since the mid-fifties when the first list processing applications and languages were developed. When Knuth systematized the accumulated knowledge about data structures in his 1968 book on Fundamental Algorithms, he devoted half the space to tree structures. During the seventies, data structures based on trees were extended to files on secondary storage and to multidimensional problems such as multi-key access. Trees also became the dominant data structure for many algorithms in the field of concrete complexity, because they are the only structures known that guarantee an O(log n) worst case bound on sequential and random access, insertion and deletion on linearly ordered sets. Recent events indicate, however, that in the coming decade the predominance of trees as all-round data structures may be challenged by address computation techniques. Various refinements and generalizations of the old programming trick called hashing have caused an unexpected extension of the domain of applicability of address computation techniques to dynamic files and multi-key access.

This paper surveys the history of data structures used for tables, files or record management systems: structures designed for efficient retrieval, insertion and deletion of single records characterized by key values chosen from linearly ordered sets. By describing a few milestones and highlights, I attempt to identify trends and speculate on future developments.