This report delineates the theory and terminology of data compression. It surveys four data compression methods--null suppression, pattern substitution, statistical encoding, and telemetry compression--and relates them to a standard statistical coding problem, i.e., the noiseless coding problem. The well defined solution to that problem can serve…

The command language features of 11 on-line information retrieval systems are presented in terms of the functional needs of a searcher sitting at a terminal. Functional areas considered are: becoming familiar with the system, receiving help when in trouble, regulating usage, selecting a data base, formulating simple queries, expressing single…