Multicriteria scheduling using fuzzy theory and tabu search

Scheduling problems are frequently encountered in manufacturing systems. The results of job scheduling can have a great impact on the throughputs of systems. To maintain a high level of productivity of the systems, many objectives have to be taken into account simultaneously while evaluating the results of a scheduling arrangement. Unfortunately, in the high-dimension environment of considering these objectives, the performance evaluation over the criteria of interest becomes rather vague. Thus, it is very difficult to apply the traditional numerical methods to construct the models, though the measurement of these may not be fully compatible with the criteria of the scheduling problems. In this paper, the linguistic values of fuzzy set theory are introduced to evaluate each criterion and to represent its relative weight for the schedules of a multicriteria environment. The basic operations for the triangular fuzzy numbers and the calculations for obtaining the ranking of each aggregated linguistic evaluation for the quality of the schedule are explained clearly. According to the complex property of scheduling problems, a heuristic approach of tabu search is applied to solve the problems. The basic mechanism and spirits of the tabu search are also interpreted here. The overall procedure of the proposed approach is addressed by a numerical example. The aim is to propose an approach that can more easily apply the multicriteria technique.