This paper presents several local search heuristics for the problem of scheduling a single machine to minimize total weighted tardiness. We introduce a new binary encoding scheme to represent solutions, together with a heuristic to decode the binary representations into actual sequences. This binary encoding scheme is compared to the usual “natural” permutation representation for descent, simulated annealing, threshold accepting, tabu search and genetic algorithms on a large set of test problems. Computational results indicate that all of the heuristics which employ our binary encoding are very robust in that they consistently produce good quality solutions, especially when multistart implementations are used instead of a single long run. The binary encoding is also used in a new genetic algorithm which performs very well and requires comparatively little computation time. A comparison of neighborhood search methods which use the permutation and binary representations shows that the permutation-based methods have a higher likelihood of generating an optimal solution, but are less robust in that some poor solutions are obtained. Of the neighborhood search methods, tabu search clearly dominates the others. Multistart descent performs remarkably well relative to simulated annealing and threshold accepting.

Time is an essential measure of performance in software development because time delays tend to fall directly to the bottom line. To address this issue, this research seeks to distinguish time-based software development practices: those managerial actions that result in faster development speed and higher productivity. This study is based upon a survey of software management practices in Western Europe and builds upon an earlier study we carried out in the United States and Japan (Integrated Manufacturing Systems, vol. 7, no. 2, 1996). We measure the extent to which managers in the USA, Japan and Europe differ in their management of software projects and also determine the tools, technology and practices that separate fast and slow developers in Western Europe.

The identification, combination, and interaction of the many factors which influence software development productivity makes the measurement, estimation, comparison and tracking of productivity rates very difficult. Through the analysis of a European Space Agency database consisting of 99 software development projects from 37 companies in a European countries, the paper seeks to provide significant and useful Information about the major factors which influence the productivity of European space, military, and industrial applications, as well as to determine the best metric for measuring the productivity of these projects. Several key findings emerge from the study. The results indicate that some organizations are obtaining significantly higher productivity than others. Some of this variation is due to the differences in the application category and programming language of projects in each company; however, some differences must also be due to the ways in which these companies manage their software development projects. The use of tools and modern programming practices were found to be major controllable factors in productivity improvement. Finally, the lines-of-code productivity metric is shown to be superior to the process productivity metric for projects in the authors' database.

In the problem of scheduling a single machine to minimize total weighted late work, there are n jobs to be processed for which each has an integer processing time, a weight and a due date. The objective is to minimize the total weighted late work, where the late work for a job is the amount of processing of this job which is performed after its due date. An O(n log n) algorithm is derived for the preemptive total weighted late work problem. For non-preemptive scheduling, efficient algorithms are derived for the special cases in which all processing times are equal and in which all due dates are equal. A pseudopolynomial algorithm is presented for the general non-preemptive total weighted late work problem. Also, a branch and bound algorithm in which lower bounds are obtained using the dynamic programming state-space relaxation method is proposed for this general problem. Computational results with the branch and bound algorithm for problems with up to 700 jobs are given. INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.