Controlling the production in an industrial organisation is very complex. There are two different reasons for this complexity. On the one hand, complexity is due to the variety in range and in level of detail of the activities that playa role in such a control (think of manufacturing process development, capacity planning, coordinating the flow of material through the production process, releasing of workorders, and scheduling). On the other hand, the production process itself may be complex (many products, many stages, complex interrelationships between resources, and uncertainty in the availability of resources). To deal with the first cause for complexity, one creates different, but coordinated levels of control. At each of these levels a specific part of the control of the production process is accounted for (see Anthony [3]). To deal with the second cause for complexity, one groups manufacturing steps into so-called production units (see Bertrand [8]). Each production unit is responsible for a specific part of the production process. Of course, these production units have to be coordinated to ensure that the products are manufactured timely and efficiently. This activity will be referred to as material coordination (see Bertrand [8]).