is a horizontal product structure diagram that shows how long it takes to buy or make a product graphically.Backward scheduling starts with the due date and works backwards to determine when work should start.The diagram shows how long it will take to build an eyeglass from the ground up, assuming that each item in the bill of materials has a one-week lead time.Forward scheduling starts from today and moves forward to determine the earliest possible job end date.In an MRP system, production can be scheduled forward or backward.The eyeglass will be completed by the third period.