【正文】 ed) revising production plans to meet expected demands and replenishment plans to assure the timely availability of raw materials and all levels of product ponents.MRP begins by piling a Bill of Materials (BOM) for each end product or ponent of interest. This is a listing of the ponents and quantities that are needed to manufacture the end product or ponent. Theoretically, the pilation of BOMs continues recursively, enumerating the subponents that are needed to manufacture each ponent, until only raw materials appear in the generated BOMs. In practice, a manufacturer may prefer to extend the BOM enumeration for only a specified number of levels and to assume that ponents and/or raw materials beneath that level are available on demand.Next, MRP requires information on the lead times associated with each manufacturing or assembly procedure that is required to produce the ponents and end products. Lead time is the time required to assemble or manufacture the needed ponents into the end product (or higherlevel ponent), and thus is the time elapsed between the point at which all needed ponents are present and the end of assembly or manufacturing. These lead times may be piled per unit of each ponent/product or may be based on predetermined batch sizes.MRP bines the BOMs, the lead times, and estimates of demand for end products to generate the Master Production Schedule, which details a schedule of assembly and production that enables the manufacturer to meet the estimated demand. This schedule addresses only the final level of assembly or production (resulting in end products), and includes both the timing and quantities of production. The Master Production Schedule serves as the basis for all further output information from MRP.Using the Master Production Schedule as a starting point, it is a conceptually simple (but putationally demanding) task to bine it with the data on lead times and BOMs to derive a schedule of ponent (and possibly raw materials) requirements, through as many levels of assembly and production as the manufacturer chooses. This schedule can account for such factors as