Research and Advances

Minimal event-node network of project precedence relations

A procedure for constructing a minimal event-node network to represent a set of precedence relations without parallel activities is presented. A minimal event-node network is an event-node network in which both the number of nodes and the number of arcs are the minima to preserve the given precedence relations. Counterexamples are given to show that the algorithm presented by A.C. Fisher, J.S. Liebman, and G.L. Nemhauser (1968) produces event-node networks which are not minimal. Since our procedure includes the set-covering problem, the time required may grow exponentially with the number of given activities.


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Research and Advances

Computers and employment

The relationship of computers and automation to employment is part of the more general relation of technological change to employment. The most obvious effect is that increases in productivity due to technology can eliminate jobs. Technology affects the individual worker, in the nature and amount of his work, and in his attitudes toward that work. Technological change affects the occupational structure of the entire labor force. Because of the central importance of these effects, the impact of technology has been the subject of extensive study by economists, sociologists, political scientists, and psychologists. Even within a single discipline, studies are often contradictory, and conclusions are colored by political overtones. We wish to delineate some of the issues, and present arguments given to support different viewpoints.

Editorial: on the ACM publications

It is proper that a professional organization periodically review its publication policy to ensure that it is fully meeting its responsibilities to its members To this purpose the President of ACM has asked the Editorial Board to formulate a five-year policy for recommendation to the Council and an ad hoc commitee of the Editorial Board is examining the question. Professor Gotlieb, through his distinguished editorial service over the past years as Editor-as-Chief of the Journal and also of Communications, has helped shape the development of ACM publications, and we are pleased to present his views in this invited editorial —M. Stuart Lynn, Editor-in-Chief
Research and Advances

Tests on a computer method for constructing school timetables

A previously proposed computer method for constructing timetables, based on an iteration involving Boolean matrices, is described. In limited tests the method has successfully produced timetables on every trial. References are given which relate the timetable problem to theorems on matrices of zeros and ones, and to theorems on bipartite graphs. Some problems of applying the method to constructing timetables in real situations are noted.

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