MRP is concerned with both production scheduling and
inventory control. It is a material control system that
attempts to keep adequate inventory levels to assure that
required materials are available when needed. MRP is
applicable in situations of multiple items with complex
bills of materials. MRP is not useful for job shops or for
continuous processes that are tightly linked. MRP is
especially suited to manufacturing settings where the
demand of many of the components and subassemblies
depend on the demands of items that face external
demands. Demands for end items are independent. In
contrast, demand for components used to manufacture end
items depend on the demands for the end items. The
distinctions between independent and dependent demands
are important in classifying inventory items and in
developing systems to manage items within each demand
classification. MRP systems were developed to cope
better with dependent demand items. The three major
inputs of an MRP system are the master production
schedule, the product structure records, and the inventory
status records. Without these basic inputs the MRP
system cannot function.