Considerable research during the last two decades has concentrated on aggregate production planning, inventory control, and scheduling. Aggregate planning procedures, which have been proposed for both manufacturing and service organizations, help determine monthly output, inventory, and manpower aggregates. Inventory and scheduling procedures, using the aggregate decisions as input, tend to focus on such short-term decisions as

• The sizing and timing of production orders for specific items,
• Sequencing of individual jobs, and
• Short-term allocations of resources to individual activities and operations. The total process of going from aggregate plans to more detailed plans can be called disaggregation.

Disaggregation is an important issue in manufacturing as well as service organizations. Depending upon the nature of the production system, disaggregation decisions in a manufacturing organization may exist on one or more of the following three levels:

• Given aggregate decisions on output and capacity, determine the timing and sizing of specific final product production quantities over the time horizon.
• Given the timing and sizing of final product production quantities, determine the timing and sizing of manufactured component quantities.
• Given the timing and sizing of component quantities, determine the short-term sequences and priorities of the jobs and the resource allocations to individual operations.