A general model of systems consisting of "control units" and "passive units" is established. These units could be instructions and data in computer programs, for example, or information processing modules and files in data management systems; other applications are also suggested. The model contains both structural and behavioral information. The sets of units of the model are partitioned, and the resulting subsets correspond to different groups of elements of real systems.

Abstract Files are frequently organized into records, and keys are associated with those records. A directory is a list of key‐address pairs, where each pair consists of a key and an address associated with that key. The addresses may be those of records in the file, or of intermediate data, such as inverted lists. A fundamental problem is searching a directory efficiently for known keys, in order to find all addresses associated with those keys. Several problems of finding keys in directories are considered. Methods of searching both ordered and unordered directories are analyzed; directories are classified as they organize unused space: compacted, distributed, or chained. Searching on ranges of key values, rather than exact key matching, is also considered. Finally, design tradeoffs among the classes of directory and searching strategies are developed.

Memory utilization and retrieval time from direct access inverted files are investigated as a function of the data base, the demands on it, and a parameter which the system designer may control. An analysis of the effects of data base characteristics and data base usage is also made for a linked list structure.