storage and retrieval operations for hundreds of part types
every day. Customer demands are supplied from the inventory
in the warehouses. When the inventory level is less than
the reorder point (taking into account the safety stock and
the average and variation of demands), it triggers the warehouse
to place purchasing orders (PO) to the manufacturers.
In this sense, as shown in Fig. 1, the order (i.e., information)
flows from customers backward to warehouse and then to
manufacturers, and the material flows in the reverse direction
from manufacturers forward to warehouse and then to
customers. Each warehouse has the following operations:
receiving, storage, picking and sorting, packaging, and shipping.
The distribution center has a WMS using bar code to
track the pallets, cases, and items