Scheplan is an expert system kernel that was developed for scheduling steel-making processes. The typical constraints in such processes are a fixed sequence of production stages, no machine conflicts among products, low waiting time, continuous use of some machines, and a resting time requirement for some machines. The approach presented for designing a schedule that satisfies the constraints, is not to obtain an optimal solution, but rather to obtain a feasible solution efficiently. The reason for this is that it is very difficult to define an evaluation function for the optimum, and that a combinatorial explosion may prevent a schedule from being obtained in a reasonable time. A cooperative schedule method is introduced in which the system efficiently generates a candidate schedule by a subscheduling and merging method, and the user evaluates and modifies the candidate schedule by interactive refinement.
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