The partial view of JIT is an approach to material control based on the view that a process should operate only when a customer signals a need for more parts from that process. When a process is operated in the JIT way, goods are produced and delivered just-in-time to be sold. This principle cascades upstream through the supply network, with subassemblies produced and delivered just-in-time to be assembled, parts fabricated and delivered just-in-time to be built into subassemblies, and materials bought and delivered just-in-time to be made into fabricated parts. Throughout the supply network, the trigger to start work is governed by demand from the customer – the next process (Schonberger, 1991). A supply network can be conceived of as a chain of customers, with each link coordinated with its neighbours by JIT signals. The whole network is triggered by demand from the end customer. Only the end customer is free to place demand whenever he or she wants; after that the system takes over.