Comparing an integrated and a standard planning and scheduling model

We compare two approaches for production planning and scheduling in a general workshop environment. In the first standard top-down approach, the planning level determines a production plan that satisfies the usual aggregate capacity constraints (i.e., the workload of each machine is less than its capacity). We show that these constraints are necessary but not sufficient, i.e., there may not exist a feasible schedule to achieve that production plan. In the second integrated approach, the planning level takes the exact capacity of the workshop into account. The aggregate capacity constraints are replaced by sufficient conditions which ensure the existence of a feasible schedule to achieve that plan.