Patent Publication Number: US-2005131779-A1

Title: Production scheduling system

Description:
TECHNICAL FIELD  
      The present invention relates to a master production scheduling system, and particularly to a master production scheduling system which carries out disposal of overstocked parts, adjustment of sales and production plans, adjustment of a parts procurement plan, etc.  
     BACKGROUND ART  
      A known technique for a master production scheduling system is disclosed in Japanese Laid-Open Patent Publication No. 11-15881 (1999). This technique relates to a master production scheduling system made up of a parts shortage eliminating apparatus and an overstocked parts eliminating apparatus. The parts shortage eliminating apparatus eliminates a parts shortage by deleting a portion of an entire production plan or purchasing additional parts. The overstocked parts eliminating apparatus, on the other hand, specifies all overstocked parts and adds production plans of products which use them to eliminate the surplus. The master production scheduling system thus revises a production plan which previously was not executable due to a parts shortage. Furthermore, the master production scheduling system minimizes overstocked parts inventory cost by adding production plans of products utilizing overstocked parts.  
      To reduce overstocked parts, the master production scheduling system using the above conventional technique comprises:  
      (1) a parts shortage estimating section for comparing gross requirements calculated from production planning information and information on a bill of materials against parts inventory information and a parts delivery schedule to estimate the types of parts in short supply and their quantity, clarifying the current parts shortage conditions;  
      (2) a parts shortage eliminating section for finding and listing products which use the above parts in short supply, and sequentially indicating to the operator whether other parts of each product are in short supply so that the operator can compare them, wherein if the operator sequentially selects the plan of each product as a target to be deleted in the order of products whose parts are in shorter supply, the parts shortage eliminating section deletes the selected plans from the entire production plan one after another until all the parts in short supply have been deleted from the production plan, turning the currently unexecutable production plan into an executable one;  
      (3) an overstocked parts estimating section for comparing gross requirements recalculated from executable production plan information and information on a bill of materials against the parts inventory information and parts purchase plan to estimate the types of overstocked parts and their quantity, clarifying the current parts surplus conditions (note: the overstocked parts obtained at this step includes the ones obtained as a result of deleting the plans of products which include parts in short supply in order to eliminate the parts shortage); and  
      (4) a parts surplus eliminating section for finding and listing products which use the above overstocked parts, and sequentially indicating to the operator whether other parts of each product are in excess so that the operator can compare them, wherein if the operator sequentially selects the plan of each product in the order of products which can be manufactured solely from overstocked parts and consume a larger number of overstocked parts, the parts surplus eliminating section adds the selected product plans to the production plan one after another as long as any more overstocked parts can be consumed, turning the current executable production plan into one which produces maximum profit (specifically, minimizing the overstocked parts inventory).  
      However, the conventional technique minimizes a surplus inventory based on evaluation of only product selling prices and surplus inventory cost. The technique does not maximize the cash flow (which is cash receipts minus cash disbursements). Therefore, when a production plan is modified (as in the case where a product is replaced by a new product, or production of an old product is ended), the conventional technique may increase loss as described below.  
      Firstly, the value of an additional order for parts necessary for product production to consume an overstocked parts inventory may exceed the product selling price, incurring gross loss which defeats the effect of a reduction in the cost incurred from parts obsolescence loss, increasing the total cost. Secondly, if the target products include many common parts, it is natural that the product production for consuming the overstocked parts inventory uses common parts used by current model products including marketable products, which leads to a shortage of common parts. As a result, it may become impossible to produce products having a high profit rate, incurring opportunity loss which defeats the effect of a reduction in the cost incurred from parts obsolescence loss, increasing the total cost. Thirdly, if a reduction in the price (cost) (obtained by utilizing overstocked parts) is smaller than a drop in the price of the product, the value of an additional order for parts necessary for product production to consume the overstocked parts inventory exceeds the proceeds from selling the overstocked parts to other companies as they are, increasing the total cost. That is, the conventional method may incur loss which defeats the effect of a reduction in a surplus inventory.  
     DISCLOSURE OF INVENTION  
      The present invention is applied when drafting a production plan which determines how to dispose of an overstocked parts inventory, selecting from the following options (measures): (1) produce products utilizing the overstocked parts and make efforts to increase the sales; (2) sell the overstocked parts as they are; and (3) abandon the overstocked parts as they are. Specifically, the object of the present invention is to provide a master production scheduling system capable of evaluating profit and loss produced when the above measures are carried out so as to prevent the total loss from increasing.  
      To accomplish the above object, the present invention is based on the following concepts (and components). The master production scheduling system comprises:  
      (1) a retired parts estimating section for comparing gross requirements for a current model calculated from production planning information and information on a bill of materials on the current model against parts inventory information and a parts delivery schedule to determine overstocked parts (used for only retired models) from among parts listed in a parts inventory and a parts delivery schedule (thereby clarifying the inventory conditions and the delivery schedule of retired parts which may become excessive after a product model is retired);  
      (2) a producible product quantity calculating section for, based on retired model information, information on a bill of materials, a retired parts inventory, and a retired parts delivery schedule, calculating a producible product quantity for a retired model (thereby clarifying the producible product quantity for each retired model which can be produced using the parts which may become excessive);  
      (3) an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating the amount of money to be paid for parts to be additionally ordered for each quantity of retired model products to be produced (thereby clarifying the relationship between each production quantity for each retired model and the value of the additional parts order);  
      (4) a retired model sales amount calculating section, based on the producible product quantity for the retired model, product selling price information, and sellable product quantity information, calculating an amount of sales for the retired model (thereby clarifying the relationship between each production quantity for each retired model and the estimated amount of sales);  
      (5) a retired parts sales estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the retired parts inventory, the retired parts delivery schedule, the parts purchasing price information, and sellable parts information, calculating estimated retired parts sales income to be earned from sales of retired parts which are not used for production of any product (thereby clarifying the relationship between each production quantity for each retired model and the estimated retired parts sales income);  
      (6) an additional manufacturing cost calculating section for, based on the producible product quantity for the retired model, the information on a bill of materials, and manufacturing cost information, calculating an additional manufacturing cost for each quantity of retired model products to be produced (thereby clarifying the relationship between each production quantity for each retired model and the additional manufacturing cost); and  
      (7) a production termination profit and loss calculating section for, based on the above retired parts inventory conditions and delivery schedule, the producible product quantity for the retired model, the value of the additional parts order for the retired model, the estimated sales amount for the retired model, the estimated retired parts sales income, and the additional manufacturing cost for the retired model, calculating profit or loss for each production quantity for the retired model (thereby clarifying the relationship between each production quantity for each retired model and the profit and loss); wherein products of the retired model continue to be produced until a production quantity has been reached at which profit is maximized (or loss is minimized) based on the relationship between each production quantity and the profit and loss clarified by the production termination profit and loss calculating section, and the remaining parts are sold as many as possible, abandoning the unsold parts; whereby when a production is ended, a retired parts surplus inventory can be disposed of with minimum loss.  
      To accomplish the above object, the present invention has a number of aspects as described below.  
      According to a first aspect of the present invention, a master production scheduling system capable of adjusting a production plan comprises: a data storage apparatus for storing production planning information on a product, information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, and retired model information; an MRP (an abbreviation for “material resource planning” indicating gross requirements) explosion apparatus for, based on the production planning information and the information on a bill of materials stored in the data storage apparatus, exploding a product to be produced into gross requirements; and a “retired model overstocked parts disposal method determining” apparatus (a determining apparatus) for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for comparing the gross requirements calculated by the MRP explosion apparatus against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; and a retired parts disposal section for, based on the value of the additional order and the production quantity (producible product quantity) for the retired model, drafting a production plan for the retired model in which the value of the additional order is minimized; whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a second aspect of the present invention, a master production scheduling system capable of adjusting a production plan comprises: a data storage apparatus for storing production planning information on a product, information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, and sellable product quantity information; an MRP (an abbreviation for “material resource planning” indicating gross requirements) explosion apparatus for, based on the production planning information and the information on a bill of materials stored in the data storage apparatus, exploding a product to be produced into gross requirements; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for comparing the gross requirements calculated by the MRP explosion apparatus against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; and a retired parts disposal section for, based on the value of the additional order, the production quantity (producible product quantity) for the retired model, the retired model product selling price information, and the sellable product quantity information, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a third aspect of the present invention, a master production scheduling system capable of adjusting a production plan comprises: a data storage apparatus for storing production planning information on a product, information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, sellable product quantity information, parts selling price information, and sellable parts information; an MRP (an abbreviation for “material resource planning” indicating gross requirements) explosion apparatus for, based on the production planning information and the information on a bill of materials stored in the data storage apparatus, exploding a product to be produced into gross requirements; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for comparing the gross requirements calculated by the MRP explosion apparatus against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; a retired parts sales estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the retired parts inventory, the retired parts delivery schedule, the parts selling price information, and the sellable parts information, calculating estimated retired parts sales income to be earned from sales of retired parts which are not used for production of any product; and a retired parts disposal section for, based on the value of the additional order, the retired model, the retired model product selling price information, and the estimated retired parts sales income, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a fourth aspect of the present invention, a master production scheduling system capable of adjusting a production plan comprises: a data storage apparatus for storing production planning information on a product, information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, sellable product quantity information, and manufacturing cost information; an MRP (an abbreviation for “material resource planning” indicating gross requirements) explosion apparatus for, based on the production planning information and the information on a bill of materials stored in the data storage apparatus, exploding a product to be produced into gross requirements; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for comparing the gross requirements calculated by the MRP explosion apparatus against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; an additional manufacturing cost calculating section for, based on the producible product quantity for the retired model, the information on a bill of materials, and the manufacturing cost information, calculating an additional manufacturing cost for each quantity of retired model products to be produced; and a retired parts disposal section for, based on the value of the additional order, the retired model, and the additional manufacturing cost, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a fifth aspect of the present invention, a product selling price determining system for determining a selling price of a product comprises: a data storage apparatus for storing production planning information on a product, information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, and manufacturing cost information; an MRP (an abbreviation for “material resource planning” indicating gross requirements) explosion apparatus for, based on the production planning information and the information on a bill of materials stored in the data storage apparatus, exploding a product to be produced into gross requirements; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for comparing the gross requirements calculated by the MRP explosion apparatus against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; and an additional manufacturing cost calculating section for, based on the producible product quantity for the retired model, the information on a bill of materials, and the manufacturing cost information, calculating an additional manufacturing cost for each quantity of retired model products to be produced; and a product selling price calculating section for, based on the value of the additional order, the retired model, and the additional manufacturing cost, calculating a product selling price at which no loss is incurred; whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with no loss.  
      According to a sixth aspect of the present invention, there is provided a production plan adjusting method for clearing out an overstocked parts inventory by first comparing a product production plan prepared beforehand against a parts inventory and a parts delivery schedule to determine the overstocked parts inventory and then carrying out a combination of one or more measures selected from among adjustment of the production plan, adjustment of a product selling price, sale of parts, cancellation of a parts order, and abandon of a parts inventory, the combination minimizing loss, the production plan adjusting method comprising the steps of: calculating gross requirements for the product production plan prepared beforehand and comparing the gross requirements against the parts inventory and the parts delivery schedule to determine a surplus part type and the quantity of inventoried parts of the surplus part type and the quantity of parts of the surplus part type to be warehoused; based on the quantity of inventoried parts of the surplus part type and the quantity of parts of the surplus part type to be warehoused, calculating a producible product quantity for a retired model; based on the overstocked parts inventory, the parts delivery schedule, the producible product quantity for the retired model, and a manufacturing cost, estimating, for each production quantity for the retired model, parts to be additionally ordered, a value of an additional order for the parts to be additionally ordered, an additional manufacturing cost, parts which are not used for the retired model, and the quantity of the parts which are not used for the retired model; calculating a sales amount for each production quantity (for the retired model) based on a selling price of the retired model, and calculating parts sales income and an unsold parts appraisal loss on an assumption that an upper limit sellable quantity of the parts which are not used are sold; and determining a production quantity for the retired model at which a difference obtained as a result of subtracting entire expenditure from entire income is maximized so as to clear out the overstocked parts inventory with minimum loss, the entire expenditure being a sum of the value of the additional order, the additional manufacturing cost, and the unsold parts appraisal loss, the entire income being a sum of the sales amount for the retired model and the parts sales income.  
      The master production scheduling systems according to the first to fourth aspects of the present invention may store a production plan of a current model as the production planning information. Furthermore, consider a case in which a production plan (information) has been already promised to the outside. In such a case, even if the production plan is of a retired model, it is necessary to produce the product. Therefore, a production plan for a retired model whose production has been already promised is treated as if it were of a current model. As a result, a seventh aspect of the present invention may be derived from any one of the first to fourth aspects, wherein the seventh aspect stores production planning information on a current model and/or production planning information on a retired model whose sale has been already promised, as the production planning information on a product.  
      Further, the product selling price determining system according to the fifth aspect of the present invention may also store a production plan of a current model as the production planning information. Furthermore, when a production plan (information) has been already promised to the outside, it is also necessary to produce the product even if the production plan is of a retired model. Therefore, a production plan for a retired model whose production has been already promised is treated as if it ware of a current model. As a result, an eighth aspect of the present invention may be derived from the fifth aspect, wherein the eighth aspect stores production planning information on a current model and/or production planning information on a retired model whose sale has been already promised, as the production planning information on a product.  
      Further, when no production plan (information) has been promised to the outside and all models are set as retired models, the entire production plan may be ignored. As a result, the following aspects (ninth to twelfth aspects) of the present invention may be derived from the second to fifth aspects, respectively.  
      According to a ninth aspect of the present invention, a master production scheduling system capable of adjusting a production plan comprises: a data storage apparatus for storing information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, and sellable product quantity information; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for setting the parts inventory information and the parts delivery schedule as information on parts listed in a retired parts inventory and a retired parts delivery schedule, both used for only a retired model; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; and a retired parts disposal section for, based on the value of the additional order and the production quantity (producible product quantity) for the retired model, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a tenth aspect of the present invention, a master production scheduling system capable of adjusting a production plan comprises: a data storage apparatus for storing information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, sellable product quantity information, parts selling price information, and sellable parts information; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for setting the parts inventory information and the parts delivery schedule as information on parts listed in a retired parts inventory and a retired parts delivery schedule, both used for only a retired model; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; a retired parts sales estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the retired parts inventory, the retired parts delivery schedule, the parts selling price information, and the sellable parts information, calculating estimated retired parts sales income to be earned from sales of retired parts which are not used for production of any product; and a retired parts disposal section for, based on the value of the additional order, the retired model, and the estimated retired parts sales income, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to an eleventh aspect of the present invention, a master production scheduling system capable of adjusting a production plan comprises: a data storage apparatus for storing information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, sellable product quantity information, and manufacturing cost information; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for setting the parts inventory information and the parts delivery schedule as information on parts listed in a retired parts inventory and a retired parts delivery schedule, both used for only a retired model; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; an additional manufacturing cost calculating section for, based on the producible product quantity for the retired model, the information on a bill of materials, and the manufacturing cost information, calculating an additional manufacturing cost for the production quantity (producible product quantity) for the retired model; and a retired parts disposal section for, based on the value of the additional order, the retired model, and the additional manufacturing cost, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a twelfth aspect of the present invention, a product selling price determining system for determining a selling price of a product comprises: a data storage apparatus for storing information on a bill of materials, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, and manufacturing cost information; and a determining apparatus for determining a disposal method for overstocked parts to be used for a retired model; wherein the determining apparatus includes: a retired parts estimating section for setting the parts inventory information and the parts delivery schedule as information on parts listed in a retired parts inventory and a retired parts delivery schedule, both used for only a retired model; a producible product quantity calculating section for, based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; an additional parts order estimating section for, based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating an amount of money to be paid for parts to be additionally ordered (a value of an additional order) for each quantity of retired model products to be produced; an additional manufacturing cost calculating section for, based on the producible product quantity for the retired model, the information on a bill of materials, and the manufacturing cost information, calculating an additional manufacturing cost for each quantity of retired model products to be produced; and a product selling price calculating section for, based on the value of the additional order, the retired model, and the manufacturing cost, calculating a product selling price at which no loss is incurred; whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with no loss.  
      Furthermore, in the following aspects (a thirteenth aspect and a fourteenth aspect), the planner drafts a production plan for a retired model while checking product selling prices, parts selling prices, and the values of additional orders.  
      According to a thirteenth aspect of the present invention, a production planning support system for helping adjust a production plan stores information on a producible product quantity for a retired model and information on a value of an additional order (which is an amount of money to be paid for parts to be additionally ordered) for each quantity of retired model products to be produced, the production planning support system displaying: a producible product quantity calculation results screen for indicating to a planner a relationship between the production quantity (producible product quantity) for the retired model and the value of the additional order; a detailed parts information screen for indicating to the planner a relationship between the production quantity for the retired model and the parts to be additionally ordered; and an additional production plan input screen for enabling the planner to register a plan while referring to the producible product quantity calculation results screen and the detailed parts information screen; wherein the production planning support system comprises: a retired parts disposal section for helping the planner to, based on the value of the additional order and the production quantity (producible product quantity) for the retired model, determine a production plan for the retired model, the planner aiming to dispose of a retired parts inventory and parts listed in a retired parts delivery schedule with minimum loss; whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a fourteenth aspect of the present invention, a production planning support system for helping adjust a production plan stores information on a producible product quantity for a retired model, information on a value of an additional order (which is an amount of money to be paid for parts to be additionally ordered) for each quantity of retired model products to be produced, and information on estimated retired parts sales income to be earned from sales of retired parts which are not used for production of any product, the production planning support system displaying: a producible product quantity calculation results screen for indicating to a planner relationships among the production quantity (producible product quantity) for the retired model, the value of the additional order, and the estimated retired parts sales income; a detailed parts information screen for indicating to the planner relationships among the production quantity for the retired model, the value of the additional order, and the parts to be sold; and an additional production plan input screen for enabling the planner to register a plan while referring to the producible product quantity calculation results screen and the detailed parts information screen; wherein the production planning support system comprises: a retired parts disposal section for helping the planner to, based on the value of the additional order, the estimated retired parts sales income, and the production quantity (producible product quantity) for the retired model, draft a plan, the planner aiming to dispose of a retired parts inventory and parts listed in a retired parts delivery schedule with minimum loss; whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      The present invention also has the following aspects (a fifteenth aspect and a sixteenth aspect) as production plan adjusting methods.  
      According to a fifteenth aspect of the present invention, a production plan adjusting method capable of adjusting a production plan comprises the steps of: storing production planning information on a product, information on a bill of materials including names of parts constituting the product and time required for manufacturing the product from the parts, parts inventory information, a parts delivery schedule, parts purchasing price information, and retired model information; based on the production planning information and the information on a bill of materials, exploding a product to be produced into gross requirements; comparing the gross requirements against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating a value of an additional order (which is an amount of money to be paid for parts to be additionally ordered) for each quantity of retired model products to be produced; and based on the value of the additional order and the producible product quantity for the retired model, drafting a production plan for the retired model in which the value of the additional order is minimized; whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to a sixteenth aspect of the present invention, a production plan adjusting method capable of adjusting a production plan comprises the steps of: storing production planning information on a product, information on a bill of materials including names of parts constituting the product and time required for manufacturing the product from the parts, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, retired model sellable product quantity information, parts selling price information, sellable parts information, and manufacturing cost information; based on the production planning information and the information on a bill of materials, exploding a product to be produced into gross requirements; comparing the gross requirements against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating a value of an additional order (which is an amount of money to be paid for parts to be additionally ordered) for each quantity of retired model products to be produced; based on the producible product quantity for the retired model, the information on a bill of materials, the retired parts inventory, the retired parts delivery schedule, the parts selling price information, and the sellable parts information, calculating estimated retired parts sales income to be earned from sales of retired parts which are not used for production of any product; based on the producible product quantity for the retired model, the information on a bill of materials, and the manufacturing cost information, calculating an additional manufacturing cost for each quantity of retired model products to be produced; and based on the value of the additional order, the producible product quantity for the retired model, the retired model product selling price information, the retired model sellable product quantity information, the estimated retired parts sales income, and the additional manufacturing cost, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      The present invention also has the following aspects (a seventeenth aspect and an eighteenth aspect) as computer-readable storage media which store a program for causing a computer to perform the above production plan adjusting methods.  
      According to a seventeenth aspect of the present invention, a computer-readable storage medium stores a program for causing a computer to perform a production plan adjusting method capable of adjusting a production plan, the program having the functions of: storing production planning information on a product, information on a bill of materials including names of parts constituting the product and time required for manufacturing the product from the parts, parts inventory information, a parts delivery schedule, parts purchasing price information, and retired model information; based on the production planning information and the information on a bill of materials, exploding a product to be produced into gross requirements; comparing the gross requirements against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating a value of an additional order (which is an amount of money to be paid for parts to be additionally ordered) for each quantity of retired model products to be produced; and based on the value of the additional order and the producible product quantity for the retired model, drafting a production plan for the retired model in which the value of the additional order is minimized; whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss.  
      According to an eighteenth aspect of the present invention, a computer-readable storage medium stores a program for causing a computer to perform a production plan adjusting method capable of adjusting a production plan, the program having the functions of: storing production planning information on a product, information on a bill of materials including names of parts constituting the product and time required for manufacturing the product from the parts, parts inventory information, a parts delivery schedule, parts purchasing price information, retired model information, retired model product selling price information, retired model sellable product quantity information, parts selling price information, sellable parts information, and manufacturing cost information; based on the production planning information and the information on a bill of materials, exploding a product to be produced into gross requirements; comparing the gross requirements against the parts inventory information and the parts delivery schedule to determine overstocked parts from among parts listed in a retired parts inventory and a retired parts delivery schedule; based on the retired model information, the information on a bill of materials, the retired parts inventory, and the retired parts delivery schedule, calculating a producible product quantity for a retired model; based on the producible product quantity for the retired model, the information on a bill of materials, the parts purchasing price information, the retired parts inventory, and the retired parts delivery schedule, calculating a value of an additional order (which is an amount of money to be paid for parts to be additionally ordered) for each quantity of retired model products to be produced; based on the producible product quantity for the retired model, the information on a bill of materials, the retired parts inventory, the retired parts delivery schedule, the parts selling price information, and the sellable parts information, calculating estimated retired parts sales income to be earned from sales of retired parts which are not used for production of any product; based on the producible product quantity for the retired model, the information on a bill of materials, and the manufacturing cost information, calculating an additional manufacturing cost for each quantity of retired model products to be produced; and based on the value of the additional order, the producible product quantity for the retired model, the retired model product selling price information, the retired model sellable product quantity information, the estimated retired parts sales income, and the additional manufacturing cost, drafting a production plan for the retired model in which profit is maximized (or loss is minimized); whereby the retired parts inventory and parts listed in the retired parts delivery schedule can be disposed of with minimum loss. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a diagram showing a configuration of apparatuses for a master production scheduling system according to the present invention.  
       FIG. 2  is a flowchart schematically showing a production plan adjustment algorithm according to the present invention.  
       FIG. 3  is an explanatory diagram showing the component parts of products A and B having common parts between them.  
       FIG. 4 ( a ) is an explanatory diagram showing an original production plan for the product A;  FIG. 4 ( b ) is an explanatory diagram showing the quantity of parts a to be warehoused; and  FIG. 4 ( c ) is an explanatory diagram showing the quantity of parts a to be inventoried.  
       FIG. 5  is an explanatory diagram showing estimated changes in the purchasing price of part a.  
       FIG. 6  is an explanatory diagram showing a list of retired models.  
       FIG. 7  is a flowchart showing the details of the algorithm executed at step  201  shown in  FIG. 2 .  
       FIG. 8 ( a ) is an explanatory diagram showing changes in the required quantity of parts a, while  FIG. 8 ( b ) is an explanatory diagram showing changes in the required quantity of parts b.  
       FIG. 9  is a flowchart showing the details of the algorithm executed at step  202  shown in  FIG. 2 .  
       FIG. 10  is a flowchart showing the details of the algorithm executed at step  203  shown in  FIG. 2 .  
       FIG. 11 ( a ) is an explanatory diagram showing the inventory of part c;  FIG. 11 ( b ) is an explanatory diagram showing the quantity of parts c to be warehoused; and  FIG. 11 ( c ) is an explanatory diagram showing an estimated inventory obtained as a result of combining the delivery schedule for part c with the original inventory of part c.  
       FIG. 12  is a flowchart showing the details of the algorithm executed at step  204  shown in  FIG. 2 .  
       FIG. 13  is an explanatory diagram showing the relationship between a production quantity and the value of an additional parts order obtained as a result of executing the flowchart shown in  FIG. 12 .  
       FIG. 14  is an explanatory diagram showing screens for helping draft a production plan.  
       FIG. 15  is an explanatory diagram showing other screens for helping draft a production plan.  
       FIG. 16  is a diagram showing a hardware configuration of the master production scheduling system according to the present invention.  
       FIG. 17  is a diagram showing another configuration of apparatuses for the master production scheduling system according to the present invention.  
       FIG. 18  is a flowchart schematically showing a production plan adjustment algorithm according to the present invention.  
       FIG. 19  is an explanatory diagram showing the component parts of products A and B having common parts between them.  
       FIG. 20 ( a ) is an explanatory diagram showing an original production plan for the product A;  FIG. 20 ( b ) is an explanatory diagram showing the quantity of parts a to be warehoused; and  FIG. 20 ( c ) is an explanatory diagram showing the quantity of parts a to be inventoried.  
       FIG. 21 ( a ) is an explanatory diagram showing estimated changes in the purchasing price of part a;  FIG. 21 ( b ) is an explanatory diagram showing changes in the selling price of the product A; and  FIG. 21 ( c ) is an explanatory diagram showing estimated changes in the selling price of part a.  
       FIG. 22 ( a ) is an explanatory diagram showing a list of retired models;  FIG. 22 ( b ) is an explanatory diagram showing the sellable product quantity for each model;  FIG. 22 ( c ) is an explanatory diagram showing the sellable part quantity for each part type; and  FIG. 22 ( d ) is an explanatory diagram showing a manufacturing cost for each model.  
       FIG. 23  is a flowchart showing the details of the algorithm executed at step  1601  shown in  FIG. 18 .  
       FIG. 24 ( a ) is an explanatory diagram showing changes in the required quantity of parts a, while  FIG. 24 ( b ) is an explanatory diagram showing changes in the required quantity of parts b.  
       FIG. 25  is a flowchart showing the details of the algorithm executed at step  1602  shown in  FIG. 18 .  
       FIG. 26  is a flowchart showing the details of the algorithm executed at step  1603  shown in  FIG. 18 .  
       FIG. 27 ( a ) is an explanatory diagram showing the inventory of part c;  FIG. 27 ( b ) is an explanatory diagram showing the quantity of parts c to be warehoused; and  FIG. 27 ( c ) is an explanatory diagram showing an estimated inventory obtained as a result of combining the delivery schedule for part c with the original inventory of part c.  
       FIG. 28  is a flowchart showing the details of the algorithm executed at step  1604  shown in  FIG. 18 .  
       FIG. 29  is a flowchart showing the details of the algorithm executed at step  2601  shown in  FIG. 28 .  
       FIG. 30  is an explanatory diagram showing the relationship between a production quantity and the value of an additional parts order obtained as a result of executing step  2601  shown in  FIG. 28 .  
       FIG. 31  is an explanatory diagram showing the relationship between a production quantity and profit and loss obtained as a result of executing step  2605  shown in  FIG. 28 .  
       FIG. 32  is an explanatory diagram showing screens for helping draft a production plan when no parts are sold.  
       FIG. 33  is an explanatory diagram showing screens for helping draft a production plan when parts are sold.  
       FIG. 34  is a flowchart showing a product selling price determination algorithm.  
       FIG. 35  is a flowchart showing the details of the algorithm executed at step  3004  shown in  FIG. 34 .  
       FIG. 36  is a diagram showing a hardware configuration of the master production scheduling system according to the present invention. 
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION  
       FIG. 1  shows a functional configuration of a master production scheduling system according to the present invention. As shown in  FIG. 1 , a master production scheduling system  100  of the present invention comprises an MRP explosion apparatus  115 , a “retired model overstocked parts disposal method determining” apparatus  103 , and a data storage apparatus  101 . It should be noted that the master production scheduling system may comprise an operator input/output apparatus  102 .  
      The above data storage apparatus  101  comprises: a production planning information storage section  104  for storing production plans drafted beforehand; a information on a bill of materials storage section  105  for storing a component parts list and production lead time (time required for manufacturing a product from its component parts) for each product; a parts inventory information storage section  106  for storing the current inventory state of each part; a parts delivery schedule storage section  107  for storing a delivery schedule on each ordered part; a parts purchasing price information storage section  108  for storing an estimated unit purchasing price of each part to be purchased in the future; and a retired model information storage section  109  for storing the names of retiring (retired) product models. An example of how data stored by each section within the data storage apparatus  101  is displayed on the operator input/output apparatus  102  will be described later.  
      The above MRP explosion apparatus  115  carries out MRP explosion. “MRP” is an abbreviation for “material resource planning”, indicating estimation of gross requirements. An MRP explosion process obtains the name of each part and its quantity needed to produce each product according to a production plan stored in the above production planning information storage section  104  and the time period in which the parts should be procured by referring to the component parts list and the production lead time of each product stored in the above information on a bill of materials storage section  105 .  
      The above “retired model overstocked parts disposal method determining” apparatus  103  comprises: a retired parts estimating section  116  for estimating the parts inventory and the parts delivery schedule for a retired model based on the output of the MRP explosion apparatus  115 ; a producible product quantity calculating section  117  for calculating a producible product quantity for the retired model based on the above parts inventory and parts delivery schedule for the retired model; an additional parts order estimating section  118  for estimating parts to be additionally ordered and the amount of money to be paid for them (the value of the additional parts order) when a quantity of products of the retired model equal to the producible product quantity are produced; and a retired parts disposal section  120  for clearing out the retired parts inventory and parts listed in the retired parts delivery schedule such that the value of the additional parts order is minimized based on the producible product quantity for the retired model and the parts to be additionally ordered and the value of the additional parts order.  
      The operator input/output apparatus  102  can indicate to the operator data stored in each section of the data storage apparatus  101 . The operator input/output apparatus  102  also can receive information for updating the data stored in each section of the data storage apparatus  101 . Furthermore, when the operator drafts a production plan for a retired model in an interactive manner, the operator input/output apparatus  102  can display a screen for helping draft the plan.  
      The master production scheduling system  100  also includes programs used for processing to indicate data to the operator input/output apparatus  102 , input data processing, etc.  
       FIG. 2  shows a production plan adjustment algorithm according to the present invention. This algorithm realizes the above “retired model overstocked parts disposing method determining” apparatus  103 .  
      With reference to  FIGS. 2 and 4  to  15 , description will be made below of a production plan adjustment according to an embodiment of the present invention by use of products A 301  and B 302  whose component parts lists are shown in  FIG. 3 . Thus, two types of products, namely product types A and B, are used as examples. The product A 301  is made up of parts a 303  and b 304 . Reference numeral L A  denotes a production lead time required for manufacturing the product A 301  from the parts a 303  and b 304 .  
      The product B 302 , on the other hand, is made up of parts a 305  and c 306 . Reference numeral L B  denotes a production lead time required for manufacturing the product B 302  from the parts a 305  and c 306 . The parts a 303  and a 305  are common parts between the products A 301  and B 302 . This information is stored in the information on a bill of materials storage section  105  in the data storage apparatus  101 .  
      It should be noted that each figure indicates data in a state in which the data is displayed on the screen of the operator input/output apparatus  102  for convenience even though the data is stored in a different form. Thus, in the present embodiment, the data configuration of information stored in the data storage apparatus  101  is indicated in a form in which the information (data) is displayed on the screen of the operator input/output apparatus  102 .  
       FIG. 4 ( a ) shows an example of production planning information stored in the production planning information storage section  104  in the data storage apparatus  101 . Specifically,  FIG. 4 ( a ) indicates the production plan of the product A 301 , wherein the horizontal axis indicates each time period of the schedule and the vertical axis indicates the number of products A 301  to be completed for each time period.  
       FIG. 4 ( b ) shows an example of a parts delivery schedule stored in the parts delivery schedule storage section  107  in the data storage apparatus  101 . Specifically,  FIG. 4 ( b ) indicates the parts delivery schedule of the part a 303  of the product A 301 , wherein the horizontal axis indicates each time period of the schedule in which parts are warehoused and the vertical axis indicates their quantity.  
       FIG. 4 ( c ) shows an example of parts inventory information stored in the parts inventory information storage section  106  in the data storage apparatus  101 . Specifically,  FIG. 4 ( c ) indicates the inventory (schedule) of the part a 303  of the product A 301 , wherein the horizontal axis indicates each time period of the schedule and the vertical axis indicates the total inventory (the number of warehoused parts minus the number of retrieved parts).  
       FIG. 5  shows an example of parts purchasing price information stored in the parts purchasing price information section  108  in the data storage apparatus  101 . Specifically,  FIG. 5  indicates changes in the purchasing price of the part a 303  of the product A 301 , wherein the horizontal axis indicates each time period of the parts delivery schedule and the vertical axis indicates the purchasing price of the part.  
       FIG. 6  shows an example of retired model information stored in the retired model information storage section  109  in the data storage apparatus  101 . In this example, the product B 302  is registered as a retired model.  
      Description will be made below of production plan adjustment carried out by a production plan adjusting system of the present invention with reference to accompanying drawings.  FIG. 2  schematically shows a production plan adjusting method.  
      As shown in  FIG. 2 , based on a predetermined production plan, the production plan adjusting system of the present invention explodes a product into required quantities of parts at step  201  and extracts overstocked parts based on the exploded required part quantities at step  202 . Step  203  calculates the number of products which can be produced (producible product quantity) for each retired model based on the overstocked parts extracted at step  202 . Step  204  calculates the value of an additional parts order for each quantity of products of each model using the producible product quantity for the model calculated at step  203 . Step  205  determines a planned production quantity for each retired model and adds it to the production plan based on the value of the additional parts order (calculated at step  204 ) for each quantity of products of each model. Step  206  determines whether any addition has been made to the planned production quantity at step  205 . If it is determined that some addition has been made to the planned production quantity, the process flow returns to step  202 . If it is determined that no addition has been made to the planned production quantity, on the other hand, the process flow ends. Steps  202  to  206  are repeated to finally determine a production quantity for each retired model.  
       FIG. 7  shows the details of step  201 , which is carried out by the MRP explosion apparatus  115 . First of all, step  701  extracts a current-model production plan based on the above production planning information and retired model information. In this example, the retired model is the product B as indicated in  FIG. 6 . Therefore, the current-model production plan is obtained as a result of removing the plan of the product B from the entire production plan. The current-model production plan is indicated by  FIG. 4 ( a ). Step  702  calculates required part quantities for a current model based on the above information on a bill of materials and current-model production plan. Specifically, from a parts list, step  702  estimates each part type and its quantity required to produce a quantity of products determined by the production plan. In the example of  FIG. 3 , 50 parts a 303  and 50 parts b 304  are needed to manufacture 50 products A 301 . As described above, since a production plan is a schedule indicating time periods (intervals) and the quantity of products to be completed in each time period, the required quantities of the parts a 303  and b 304  for each time period are calculated based on the production plan of the product A, considering each production lead time. The required quantities of the parts a 303  and b 304  are calculated as indicated by FIGS.  8 ( a ) and  8 ( b ). In each figure, the horizontal axis indicates each time period of the schedule in which parts are needed, while the vertical axis indicates the required quantity of the parts.  
       FIG. 9  shows the details of step  202 . Step  202  is carried out by the above retired parts estimating section  116 . First of all, step  901  starts a loop consisting of the subsequent steps  902  through  909  to be repeated for all part types. The next step  902  starts another loop consisting of the subsequent steps  903  through  908  to be repeated for each time period of the schedule in which parts are need. For a target part type and in a target time period, step  903  subtracts the required part quantity from the quantity of parts to be warehoused. However, if the target time period is the time period t 1  in the figure, step  903  subtracts the required part quantity from the sum of the inventory (quantity) up to that time period and the quantity of parts to be warehoused. At that time, when the required part quantity is larger than the quantity of the parts to be warehoused, step  903  subtracts only a part quantity equal to the quantity of the parts to be warehoused.  
      Then, step  904  subtracts the quantity of the parts to be warehoused (which is the quantity before the above subtraction at step  903 ) from the required part quantity to produce a remaining required part quantity. The remaining required part quantity indicates the part quantity by which the required part quantity exceeds the quantity of the parts to be warehoused for the target time period. Then, step  905  checks whether the remaining required part quantity is larger than 0. If it is not larger than 0, the processing flow proceeds to step  902 , and the required part quantity for the next time period is subtracted. If the remaining required part quantity is larger than 0, on the other hand, the processing flow proceeds to step  906 .  
      Step  906  determines whether the target time period in which parts are needed is the time period t 1 . If it is determined that the target time period is the time period t 1 , the processing flow proceeds to step  909 . If it is determined that the target time period is not the time period t 1 , on the other hand, the processing flow proceeds to step  907 . Step  907  moves back the target time period to the previous time period (for the remaining required part quantity). For example, if the required part quantity is larger than the quantity of parts to be warehoused in the time period t 5 , the processing flow proceeds to a processing step at which the remaining required part quantity is subtracted from the quantity of parts to be warehoused in the time period t 4 .  
      Then, step  908  newly sets the remaining required part quantity as the required part quantity, and the processing flow proceeds to step  909 . Step  909  determines whether steps  903  through  908  have been repeated for all time periods of the schedule to process the required part quantities. If it is determined that the steps have not yet been repeated for all time periods to process the required part quantities, the processing flow returns to step  902 . If it is determined that the steps have been repeated for all time periods to process the required part quantities, the processing flow proceeds to step  910 . Step  910  determines whether steps  902  through  909  have been repeated for all part types. If it is determined that the steps have not yet been repeated for all part types, the processing flow returns to step  901 . If it is determined that the steps have been repeated for all part types, the processing flow proceeds to step  911 . Step  911  sets as an overstocked parts quantity the quantity of parts to be warehoused for each time period from which any required part quantity has not been subtracted (or, for the time period t 1 , the sum of the inventory up to that time period and the quantity of parts to be warehoused for that time period), and the processing flow ends.  
      As described above, steps  903  through  908  are repeated so as to subtract each required part quantity from the quantity of parts to be warehoused in the corresponding time period and thereby calculate the quantity of parts to be warehoused which are not used for a current model, that is, the (quantity of) overstocked parts.  
       FIG. 10  shows the details of step  203 . This example shows a method for calculating the number of products which can be produced (a producible product quantity) for each model. First of all, step  1101  starts a loop consisting of the subsequent steps  1102  through  1115  to be repeated for each retired model.  
      Step  1102  estimates the inventory schedule of each part type based on the above current parts inventory and parts delivery schedule. The inventory schedule is obtained by adding the quantity of parts to be warehoused to the current parts inventory over all time periods.  FIG. 11  shows an example of this estimation.  FIG. 11 ( a ) shows the inventory quantity of the part c 306 . Specifically, the horizontal axis indicates each time period of the schedule, while the vertical axis indicates the inventory quantity, taking into no account the quantity of parts to be warehoused or retrieved. In  FIG. 11 ( b ), the horizontal axis indicates each time period of the schedule, while the vertical axis indicates the quantity of the parts c 306  to be warehoused. Specifically,  FIG. 11 ( b ) indicates that parts will be warehoused in the time periods t 1 , t 6 , and t 11 . In  FIG. 11 ( c ), the horizontal axis indicates each time period of the schedule, while the vertical axis indicates the inventory quantity of the part c 306  including the quantity of parts to be warehoused shown in  FIG. 11 ( b ).  
      Then, step  1103  starts a loop consisting the subsequent steps  1104  through  1114  to be repeated for each time period of the production schedule. The length of each time period for which the loop is repeated can be freely set by the operator. Then, step  1104  sets the initial planned product quantity to ∞. After that, step  1105  explodes a target model (product) into required part quantities based on the above information on a bill of materials.  
      Then, step  1106  starts a loop consisting of the subsequent steps  1107  through  1112  to be repeated for each component part type. Step  1107  determines whether the above exploded required part quantity for each component part type is larger than the estimated part inventory quantity for that component part type. If it is determined at step  1107  that the required part quantity is larger than the estimated part inventory quantity, the processing flow proceeds to step  1108 . If it is determined that the required part quantity is not larger than the estimated part inventory quantity, on the other hand, the processing flow proceeds to step  1110 .  
      Step  1108  checks whether parts of a target part type can be delivered in time if the order is newly issued at this time point.  
      If the parts can be delivered in time, the processing flow proceeds to step  1109 .  
      If the parts cannot be delivered in time, the processing flow proceeds to step  1110 . Step  1109  sets the quantity of parts of the target part type which can be procured to be equal to the required part quantity. Step  1110  sets the quantity of parts of the target part type which can be procured to be equal to the estimated part inventory quantity. Both steps  1109  and  1110  proceed to step  1111 .  
      Step  1111  divides the procurable part quantity for the target part type by the number of parts of that part type constituting each product to obtain a part-basis producible product quantity for the target part type. Then, step  1112  updates the parts inventory schedule for all time periods after this time period. Specifically, step  1112  subtracts the estimated parts inventory for this time period from the estimated parts inventory for each time period after this time period and sets each result as the updated estimated parts inventory for a respective time period.  
      Step  1113  determines whether the loop consisting of steps  1107  through  1112  has been repeated for all component part types. If it is determined that the loop consisting of steps  1107  through  1112  has been repeated for all component part types, the processing flow proceeds to step  1114 . If it is determined that the loop has not yet been repeated for all component part types, on the other hand, the processing flow returns to step  1106 . Step  1114  selects the minimum value from among the part-basis producible product quantities as the producible product quantity.  
      Then, step  1115  determines whether the loop consisting of steps  1104  through  1114  has been repeated for all time periods of the production schedule. If it is determined that the loop consisting of steps  1104  through  1114  has been repeated for all time periods of the production schedule, the processing flow proceeds to step  1116 . If it is determined that the loop has not yet been repeated for all time periods of the production schedule, the processing flow returns to step  1103 . Step  1116  determines whether the loop consisting of steps  1102  through  1115  has been repeated for all retired models. If it is determined that the loop consisting of steps  1102  through  1115  has been repeated for all retired models, the processing flow ends. If it is determined that the loop has not yet been repeated for all retired models, the processing flow returns to step  1101 .  
      As described above, by carrying out calculations for each model and each time period, it is possible to calculate the producible product quantity for each model in the case where all overstocked parts are assigned to the model. It should be noted that in addition to the above method in which a producible product quantity is calculated for each model, it is possible to employ a “priority-model-basis producible product quantity calculating method” comprising the steps of: giving priority to each retired model; calculating the producible product quantity for the retired model having the highest priority; and calculating the producible product quantity for the retired model having the second highest priority by use of the remaining parts (and so on). Furthermore, the producible product quantity for each retired model can be determined by using as an evaluation criterion an additional parts order quantity or gain and loss (described later) and employing a gradient method or a linear programming method such that the item selected as the evaluation criterion has a best value.  
       FIG. 12  shows the details of step  204 . This step is performed by the additional parts order estimating section  118 . First of all, step  1201  starts a loop consisting of the subsequent steps  1202  through  1213  to be repeated for all models. Step  1202  starts a loop consisting of the subsequent steps  1203  through  1211  to be repeated for every production quantity starting from 0 up to the producible product quantity calculated at step  203 .  
      Step  1203  explodes a target production quantity of products into required part quantities based on the information on a bill of materials. Then, step  1204  starts a loop consisting of the subsequent steps  1205  through  1210  to be repeated for all component part types.  
      Step  1205  determines whether the required part quantity for a target component part type is larger than the (corresponding) estimated parts inventory quantity. If it is determined that the required part quantity for the target component part type is larger than the estimated parts inventory quantity, the processing flow proceeds to step  1206 . If it is determined that the required part quantity for the target component part type is not larger than the estimated parts inventory quantity, on the other hand, the processing flow proceeds to step  1208 . Step  1206  checks whether parts of the target part type can be delivered in time if the order is issued at this time point, that is, whether a new order for parts of the target part type can be placed. If the new order can be placed, the processing flow proceeds to step  1207 . If the new order cannot be placed, on the other hand, the processing flow proceeds to step  1208 . Step  1207  sets the additional order quantity to be equal to the required part quantity for the target part type minus the estimated part inventory quantity, and the processing flow proceeds to step  1209 . Step  1208  sets the additional order quantity to 0, and the processing flow proceeds to step  1209 . Step  1209  calculates the value of the additional order for the target part type based on the additional order quantity. The value of the additional order for the target part type is obtained by multiplying the additional order quantity by the purchasing price of the target part type. Then, step  1210  adds the value of the additional order for the target part type to the value of the additional parts order (the total additional order) so that after the loop has been repeated for all component part types, the value of the additional parts order for each production quantity can be obtained.  
      Then, step  1211  determines whether the loop consisting of steps  1205  through  1210  has been repeated for all component part types. If it is determined that the loop has been repeated for all component part types, the processing flow proceeds to step  1212 . If it is determined that the loop has not yet been repeated for all component part types, on the other hand, the processing flow returns to step  1204 . Step  1212  determines whether the loop consisting of steps  1203  through  1211  has been repeated for all possible production quantities. If it is determined that the loop has been repeated for all possible production quantities, the processing flow proceeds to step  1213 . If it is determined that the loop has not yet been repeated for all possible production quantities, the processing flow returns to step  1202 . Step  1213  determines whether the loop consisting steps  1202  through  1212  has been repeated for all models. If it is determined that the loop has been repeated for all models, the processing flow ends. If it is determined that the loop has not yet been repeated for all models, on the other hand, the processing flow returns to step  1201 . A result from the above processing is shown in  FIG. 13 . In the figure, the horizontal axis indicates the production quantity, while the vertical axis indicates the value of the additional parts order.  
      Then, step  205  determines a quantity to be added to the planned production quantity based on the value of the additional parts order for each model obtained at step  204 . This determination may be made by the operator interactively with the above operator input/output apparatus  102 . Or alternatively, based on the value of the additional parts order for each model, the above retired parts disposal section  120  may determine a production quantity at which the value of the additional parts order is minimized. An example of determination made interactively by the operator will be described later. The determined planned production quantity is supplied to step  206 . Step  206  determines whether any addition has been made to the original planned production quantity.  
      If it is determined that some addition has been made to the planned production quantity, the processing flow returns to step  202 . If it is determined that no addition has been made to the planned production quantity, on the other hand, the processing flow ends. Step  202  includes the steps of: when overstocked parts are estimated, exploding a quantity of products equal to the above quantity added to the planned production quantity at step  205  based on the information on a bill of materials; and subtracting the resultant required part quantity for the additional production plan from the surplus part quantity to obtain overstocked parts (quantity) after the above addition to the production plan.  
      As described above, steps  202  through  206  are repeated, and then evaluation is made by use of the value of the additional parts order calculated at step  204  to determine a retired model production plan and the number of parts to be sold (for each part type). With this arrangement, it is possible to dispose of the retired parts inventory and retired parts to be warehoused with a minimum of the value of the additional parts order.  
      Description will be made below of an example in which the operator (planner) interactively drafts a production plan for a retired model with reference to  FIG. 14 .  
      First, a producible product quantity calculation results screen  1401  is displayed to the planner. This screen indicates the producible product quantity for each model in each time period and the value of the corresponding additional (parts) order. On the screen, the planner selects a model whose production plan is to be drafted by comparing the selling prices of models to one another. If the operator (planner) selects a field of a target model by use of a mouse or a keyboard and further selects an Add Plan button  1404  by use of a mouse or a keyboard, the producible product quantity for the target model in each time period and the value of the corresponding additional (parts) order are copied to an additional production plan input screen  1402 .  
      On the additional production plan input screen  1402 , the field to which the producible product quantity for the target model in each time period is copied is referred to as an additional production plan field. On the additional production plan input screen  1402 , as an additional production plan, the planner enters a value, which is smaller than a respective producible product quantity, in the additional production plan field of each model for each time period by use of a mouse or a keyboard. When determining the value, if the planner selects the additional production plan field of a target model for a target time period by use of a mouse or a keyboard and further selects a Detail button  1405  by use of a mouse or a keyboard, a detailed parts information screen  1403  is displayed.  
      The detailed parts information screen  1403  displays, for each (possible) production quantity, the names of parts to be additionally ordered for the target model in the target time period and the value of the order. The planner checks each production quantity, the names of parts to be additionally ordered, the value of the order, and the selling price of the product, and selects a desired production quantity by use of a mouse or a keyboard. After selecting the desired product quantity, if the planner selects an Enter button  1408  by use of a mouse or a keyboard, the selected product quantity (for the production plan) is copied to the production quantity field (the additional production plan field) of the target model for the target time period on the additional production plan input screen  1402 . On the other hand, if the planner does not want to produce any products of the target model in the target and subsequent time periods, the planner selects the production quantity field of the target model for the target time period on the additional production plan input screen  1402  by use of a mouse or a keyboard and further selects a “No Production For Subsequent Time Periods” button  1406  by use of a mouse or a keyboard to set a value of 0 for the production quantity fields of the target model for the target time period and all the subsequent time periods on the additional production plan input screen  1402 .  
      After drafting a final retired model production plan by repeating the above operation for each model, the planner selects an Enter Plan button  1407  on the additional production plan input screen  1402  by use of a mouse or a keyboard to decide an additional production plan for each retired model.  
      Description will be made below of another example in which the operator (planner) also interactively drafts a production plan for a retired model with reference to  FIG. 15 .  
      First, a producible product quantity calculation results screen  1411  is displayed to the planner. This screen indicates the producible product quantity for each model in each time period and the value of the corresponding additional (parts) order. Furthermore, a Check button  1417  is provided for each model on the screen. On the screen, the planner selects a model whose production plan is to be drafted by comparing the selling prices of models to one another. If the planner selects a field of a desired model on the screen by use of a mouse or a keyboard and further selects an Add Plan button  1414  by use of a mouse or a keyboard, the model is selected as a target whose additional production plan is to be drafted, and the corresponding Check button  1417  is selected (as indicated in black in the figure). On the other hand, if the planner selects a field of the desired model on the screen by use of a mouse or a keyboard and further selects a Delete Plan button  1415  by use of a mouse or a keyboard, the model is deselected and is no longer a target whose additional production plan is to be drafted, and the corresponding Check button  1417  is deselected (as indicated in white in the figure). If the planner selects an Edit button  1416  by use of a mouse or a keyboard, the producible product quantity (for each time period) of the model whose Check button  1417  has been selected and the value of the corresponding additional (parts) order are copied to an additional production plan input screen  1412 .  
      On the additional production plan input screen  1412 , the field to which the producible product quantity for the target model in each time period is copied is referred to as an additional production plan field. On the additional production plan input screen  1412 , as an additional production plan, the planner enters a value, which is smaller than a respective producible product quantity, in the additional production plan field of each model for each time period by use of a mouse or a keyboard. When determining the value, if the planner selects the additional production plan field of a target model for a target time period by use of a mouse or a keyboard and further selects a Detail button  1418  by use of a mouse or a keyboard, a detailed parts information screen  1413  is displayed.  
      The detailed parts information screen  1413  displays, for each (possible) production quantity, the names of parts to be additionally ordered for the target model in the target time period and the value of the order. The planner checks each production quantity, the names of parts to be additionally ordered, the value of the order, and the selling price of the product, and selects a desired product production quantity by use of a mouse or a keyboard. After selecting the desired product production quantity, if the planner selects an Enter button  1422  by use of a mouse or a keyboard, the selected production quantity (for the production plan) is copied to the production quantity field (the additional production plan field) of the target model for the target time period on the additional production plan input screen  1412 . On the other hand, if the planner does not want to produce any products of the target model in the target and subsequent time periods, the planner selects the production quantity field of the target model for the target time period on the additional production plan input screen  1412  by use of a mouse or a keyboard and further selects a “No Production For Subsequent Time Periods” button  1419  by use of a mouse or a keyboard to set a value of 0 for the production quantity fields of the target model for the target time period and all the subsequent time periods on the additional production plan input screen  1412 .  
      After drafting a final retired model production plan by repeating the above operation for each model, the planner selects an Enter Plan button  1420  on the additional production plan input screen  1412  by use of a mouse or a keyboard to decide an additional production plan for each retired model. On the additional production plan input screen  1412 , if the planner wants to change the model selected as the target whose additional production plan is to be drafted, the planner selects a Select Target button  1421  by use of a mouse or a keyboard. Since selecting the Select Target button  1421  displays the producible product quantity calculation results screen  1411 , the planner can change the model selected as the target whose additional production plan is to be drafted, as described above.  
      Description will be made below of a variation of the above example described with reference to FIGS.  1  to  15 . In this example, no production plan (information) has been promised to the outside, and therefore it can be assumed that all models to be produced are retired models. In such a case, both the required parts explosion processing at step  201  and the overstocked parts extraction processing at step  202  shown in  FIG. 2  may be omitted. The retired parts estimating section  116  may set both the parts inventory information stored in the parts inventory information storage section  106  and the parts delivery schedule stored in the parts delivery schedule storage section  107  as information on parts used for only retired models. Then, the producible product quantity calculating section  117  may calculate the producible product quantity for each retired model.  
      Description will be made below of another variation of the above example described with reference to FIGS.  1  to  15 . In this example, a production plan (information) has already been promised to the outside, and therefore it is necessary to execute the production plan even if it is of a retired model. In such a case, in the required parts explosion processing at step  201  shown in  FIG. 2 , the MRP explosion apparatus  115  may treat the production plan of a retired model whose production has been promised, as that of a current model.  
      Description will be made below of still another variation of the above example described with reference to FIGS.  1  to  15 . In this example, a production plan of a new model is stored as production planning information. In such a case, in the required parts explosion processing at step  201  shown in  FIG. 2 , the MRP explosion apparatus  115  may treat the production plan of a new model as that of a current model.  
       FIG. 16  shows the hardware configuration of the master production scheduling system  100  shown in  FIG. 1 .  
      In the figure, a computer  1600  comprises: a bus  1611 ; a main unit  1612  connected to the bus  1611 ; an external storage apparatus  1613  connected to the bus  1611 ; an input apparatus  1614  connected to the bus  1611 ; and an output apparatus  1615  connected to the bus  1611 . The main unit  1612  includes a main storage unit  16121  and a CPU (Central Processing Unit)  16122 .  
      In the computer  1600 , the main storage unit  16121  stores various programs and data necessary to execute these programs. The CPU  16122  executes a program stored in the main storage unit  16121  using data stored in the main storage unit  16121 . The external storage apparatus  1613  may have a capacity larger than that of the main storage unit  16121 . Programs and data to be stored in the main storage unit  16121  may be stored in the external storage apparatus  1613 , and then read out from the external storage apparatus  1613  into the main storage unit by the CPU  16122  as necessary. As the external storage apparatus  1613 , it is possible to use a floppy disk, which is a portable medium, a CD-ROM (Compact Disk Read-Only Memory), etc. in addition to a hard disk device.  
      In the computer  1600 , the input apparatus  1614  is made up of an input control section (not shown) and an input section (not shown), such as a mouse or a keyboard, connected to the input control section. The input apparatus  1614  receives information entered by the operator by use of the input section such as a mouse or a keyboard. The output apparatus  1615  is made up of an output control section (not shown) and an output section (not shown), such as a display or a printer, connected to the output control section. The output apparatus  1615  can output to the output section, such as a display or a printer, data read from the external storage apparatus  1613  into the main storage unit  16121  by the CPU  16122 . The output apparatus  1615  also can output a program execution result by the CPU  16122  to the output section such as a display or a printer.  
      Each apparatus in  FIG. 1  described above is implemented by the components in  FIG. 16  as follows.  
      The external storage apparatus  1613  realizes a function of the following sections in the data storage apparatus  101  to permanently store temporarily-held information: the production planning information storage section  104 , the information on a bill of materials storage section  105 , the parts inventory information storage section  106 , the parts delivery schedule storage section  107 , the parts purchasing price information storage section  108 , and the retired model information storage section  109 . The main storage unit  16121  on the other hand, realizes another function of the above sections in which the operator refers to or updates stored information, or the operator registers new information.  
      The MRP explosion apparatus  115  and the retired parts estimating section  116 , the producible product quantity calculating section  117 , the additional parts order estimating section  118 , and the retired parts disposal section  120  all included in the “retired model overstocked parts disposal method determining” apparatus  103  are implemented by performing the steps of: storing into the external storage apparatus  1613  programs designed to carry out the operations of the above apparatuses and sections; reading these programs from the external storage apparatus  1613  into the main storage unit  16121 ; and executing the programs by use of the CPU  16122 . When interactively drafting a production plan of a retired model, the operator can enter an instruction from the input apparatus  1614  while displaying the display screens as shown in  FIGS. 14 and 15  in the output apparatus  1615  so that the production plan is drafted based on the entered instruction.  
      The operator input/output apparatus  102  is implemented by the input apparatus  1614  and the output apparatus  1615 .  
      It should be noted that the following hardware configuration, which is a variation of the above hardware configuration, may be employed. A plurality of computers are connected to one another such that they can exchange data. With this arrangement, the MRP explosion apparatus  115  and the “retired model overstocked parts disposal method determining apparatus”  1503  may be each implemented by a separate computer.  
       FIG. 17  shows another functional configuration of the master production scheduling system according to the present invention. As shown in  FIG. 17 , the master production scheduling system  1500  of the present invention comprises an MRP explosion apparatus  1515 , a “retired model overstocked parts disposal method determining apparatus”  1503 , and a data storage apparatus  1501 . It should be noted that the master production scheduling system  1500  may comprise an operator input/output apparatus  1502 .  
      The above data storage apparatus  1501  comprises: a production planning information storage section  1504  for storing production plans drafted beforehand; a information on a bill of materials storage section  1505  for storing a component parts list for each product; a parts inventory information storage section  1506  for storing the current inventory state of each part; a parts delivery schedule storage section  1507  for storing a delivery schedule on each ordered part, a parts purchasing price information storage section  1508  for storing an estimated unit purchasing price of each part to be purchased in the future; a retired model information storage section  1509  for storing the names of retiring (retired) product models; a product selling price information storage section  1510  for storing an estimated selling price of each product model; a sellable product quantity information storage section  1511  for storing a sellable product quantity for each retired model on which the sales division agrees; a parts selling price information storage section  1512  for storing an estimated selling price of each part; a sellable parts information storage section  1513  for storing an estimated sellable part quantity for each part type to be sold in the future; and a manufacturing cost information storage section  1514  for storing the manufacturing cost of each product. An example of how data stored by each section within the data storage apparatus  1501  is displayed on the operator input/output apparatus  1502  will be described later.  
      The above MRP explosion apparatus  1515  carries out MRP explosion. “MRP” is an abbreviation for “material resource planning”, indicating estimation of gross requirements. An MRP explosion process obtains the name of parts and their quantity needed to produce each product according to a production plan stored in the above production planning information storage section  1504  and the time periods in which the parts should be procured by referring to the component parts list and the production lead time of each product stored in the above information on a bill of materials storage section  1505 .  
      The above “retired model overstocked parts disposal method determining” apparatus  1503  comprises: a retired parts estimating section  1516  for estimating the parts inventory and the parts delivery schedule for a retired model based on the output of the MRP explosion apparatus  1515 ; a producible product quantity calculating section  1517  for calculating a producible product quantity for the retired model based on the above parts inventory and parts delivery schedule for the retired model; an additional parts order estimating section  1518  for estimating parts to be additionally ordered and the amount of money to be paid for them (the value of the additional parts order) when a quantity of products of the retired model equal to the producible product quantity are produced; a retired model-sales amount estimating section  1519  for calculating the amount of sales obtained when a quantity of products of the retired model equal to the producible product quantity are sold; a retired parts selling schedule estimating section  1522  for calculating the estimated quantity of retired parts to be sold after a quantity of products of the retired model equal to the producible product quantity are produced and the estimated amount of sales of the retired parts; an additional manufacturing cost calculating section  1523  for calculating an additional manufacturing cost incurred when a quantity of products of the retired model equal to the producible product quantity are produced; a retired parts disposal section  1520  for clearing out the above retired parts inventory and retired parts delivery schedule such that entire loss is reduced based on the producible product quantity for the retired model, the additional parts-order, the amount of the sales of retired model products, the retired parts selling schedule, and the additional manufacturing cost; and a product selling price calculating section  1521  for calculating the selling price of the retired model to clear out the retired parts inventory and retired parts delivery schedule such that the entire loss is reduced based on the producible product quantity for the retired model, the additional parts order, the retired parts selling schedule, and the additional manufacturing cost.  
      The operator input/output apparatus  1502  can indicate to the operator data stored in each section of the data storage-apparatus  1501 . The operator input/output apparatus  1502  can receive information for updating the data stored in each section of the data storage apparatus  1501 . Furthermore, when the operator drafts a production plan for a retired model in an interactive manner, the operator input/output apparatus  1502  can display a screen for helping draft the plan.  
      The master production scheduling system  1500  also includes programs used for processing for indicating data to the operator input/output apparatus  1502 , input data processing, etc.  
       FIG. 18  shows a production plan adjustment algorithm according to the present invention. This algorithm realizes the above “retired model overstocked parts disposal method determining” apparatus  1503 .  
      With reference to  FIGS. 18 and 20  to  35 , description will be made below of a production plan adjustment according to an embodiment of the present invention by use of products A 1701  and B 1702  whose component parts lists are shown in  FIG. 19 . Thus, two types of products, namely product types A and B, are used as examples. The product A 1701  is made up of parts a 1703  and b 1704 . Reference numeral L A  denotes a production lead time required for manufacturing the product A 1701  from the parts a 1703  and b 1704 . The product B 1702 , on the other hand, is made up of parts a 1705  and c 1706 . Reference numeral L B  denotes a production lead time required for manufacturing the product B 1702  from the parts a 1705  and c 1706 . The parts a 1703  and a 1705  are common parts between the products A 1701  and B 31702 . This information is stored in the information on a bill of materials storage section  1505  in the data storage apparatus  1501 . It should be noted that each figure indicates data in a state in which the data is displayed on the operator input/output apparatus  1502  for convenience even though the data is stored in a different form. Thus, in the present invention, the data configuration of information stored in the data storage apparatus  1501  is indicated in a form in which the information (data) is displayed on the screen of the operator input/output apparatus  1502 .  
       FIG. 20 ( a ) shows an example of production planning information stored in the production planning information storage section  1504  in the data storage apparatus  1501 . Specifically,  FIG. 20 ( a ) indicates the production plan of the product A 1701 , wherein the horizontal axis indicates each time period of the schedule and the vertical axis indicates the number of products A 1701  to be completed for each time period.  
       FIG. 20 ( b ) shows an example of a parts delivery schedule stored in the parts delivery schedule storage section  1507  in the data storage apparatus  1501 . Specifically,  FIG. 20 ( b ) indicates the parts delivery schedule of the part a 1703  of the product A 1701 , wherein the horizontal axis indicates each time period of the parts delivery schedule and the vertical axis indicates the quantity of the parts a 1703  to be warehoused.  
       FIG. 20 ( c ) shows an example of parts inventory information stored in the parts inventory information storage section  1506  in the data storage apparatus  1501 . Specifically,  FIG. 20 ( c ) indicates the parts inventory of the part a 1703  of the product A 1701 , wherein the horizontal axis indicates each time period of the schedule and the vertical axis indicates the total inventory (the number of warehoused parts minus the number of retrieved parts).  
       FIG. 21 ( a ) shows an example of parts purchasing price information stored in the parts purchasing price information storage section  1508  in the data storage-apparatus  1501 . Specifically,  FIG. 21 ( a ) indicates changes in the parts purchasing price of the part a 1703  of the product A 1701 , wherein the horizontal axis indicates each time period of the parts delivery schedule and the vertical axis indicates the purchasing price of the part.  
       FIG. 21 ( b ) shows an example of product selling price information stored in the product selling price information storage section  1510  in the data storage apparatus  1501 . Specifically,  FIG. 21 ( b ) indicates changes in the product selling price of the product A 1701 , wherein the horizontal axis indicates each time period of the product order acceptance schedule and the vertical indicates the selling price of the product.  
       FIG. 21 ( c ) shows an example of parts selling price information stored in the parts selling price information storage section  1513  in the data storage apparatus  1501 . Specifically,  FIG. 21 ( c ) indicates changes in the parts selling price of the part a 1703  of the product A 1701 , wherein the horizontal axis indicates each time period of the parts selling schedule and the vertical axis indicates the selling price of the part.  
       FIG. 22 ( a ) shows an example of retired model information stored in the retired model information storage section  1509  in the data storage apparatus  1501 . In this example, the product B 1702  is registered as a retired model.  
       FIG. 22 ( b ) shows an example of sellable product quantity information stored in the sellable product quantity information storage section  1511  in the data storage apparatus  1501 . In this example, the estimated sellable product quantity for the product B 1702 , which is a retired model, is registered.  
       FIG. 22 ( c ) shows an example of sellable part quantity information stored in the sellable parts information storage section  1513  in the data storage apparatus  1501 . In this example, the estimated sellable quantity of the parts c 1706 , which are used in only the product B 1702 , is registered.  
       FIG. 22 ( d ) shows an example of product manufacturing cost information stored in the manufacturing cost information storage section  1514  in the data storage apparatus  1501 . In this example, the manufacturing costs of the products A 1701  and B 1702  are registered.  
      Description will be made below of production plan adjustment carried out by a production plan adjustment system of the present invention with reference to accompanying drawings.  FIG. 18  schematically shows a production plan adjustment method.  
      As shown in  FIG. 18 , based on a predetermined production plan, the production plan adjustment system of the present invention explodes a product into required quantities of parts at step  1601  and extracts overstocked parts based on the exploded required part quantities at step  1602 . Step  1603  calculates the number of products which can be produced (producible product quantity) for each retired model based on the overstocked parts extracted at step  1602 . Step  1604  calculates profit or loss for each quantity of products of each model based on the producible product quantity for each retired model calculated at step  1603 . Step  1605  determines a production quantity and the quantity of parts to be sold for each retired model and adds them to the production plan based on the profit or loss for each quantity of products of each model obtained at step  1604 . Step  1606  determines whether any addition has been made to the planned production quantity at step  1605 . If it is determined that any addition has been made to the planned production quantity, the process returns to step  1602 . If it is determined that no addition has been made to the planned production quantity, on the other hand, the process ends.  
      Steps  1602  through  1606  are repeated so as to finally determine a production quantity and the quantity of parts to be sold for each retired model.  
       FIG. 23  shows the de-tails of step  1601 , which is carried out by the MRP explosion apparatus  1515 . First of all, step  2101  extracts a current-model production plan based on the above production planning information and retired model information. In this example, the retired model is the product B as indicated in  FIG. 22 . Therefore, the current-model production plan is obtained as a result of removing the plan of the product B from the entire production plan. The current-model production plan is indicated by  FIG. 20 ( a ). Step  2102  calculates required part quantities for the current model based on the above information on a bill of materials and current-model production plan. Specifically, from a parts list, step  2102  estimates each part type and its quantity required for producing the quantity of products (of each model) specified by the production plan. In the example of  FIG. 19 , 50 parts a 1703  and 50 parts b 1704  are needed to manufacture 50 products A 1701 . As described above, since a production plan is a schedule indicating time periods (intervals) and the quantity of products to be completed in each time period, the required quantities of the parts a 1703  and b 1704  for each time period are calculated based on the production plan of the product A, considering each production lead time. The required quantities of the parts a 1703  and b 704  are calculated as indicated by FIGS.  24 ( a ) and  24 ( b ). In each figure, the horizontal axis indicates each time period of the schedule in which parts are needed, while the vertical axis indicates the required quantity of the parts.  
       FIG. 25  shows the details of step  1602 . Step  1602  is carried out by the above retired parts estimating section  1516 . First of all, step  2301  starts a loop consisting of the subsequent steps  2302  through  2309  to be repeated for all part types. The next step  2302  starts another loop consisting of the subsequent steps  2303  through  2308  to be repeated for each time period in which parts are needed.  
      For a target part type and in a target time period, step  2303  subtracts the required part quantity from the quantity of parts to be warehoused. However, if the target time period is the time period t 1  in the figure, step  2303  subtracts the required part quantity from the sum of the inventory (quantity) up to that time period and the quantity of parts to be warehoused. At that time, when the required part quantity is larger than the quantity of parts to be warehoused, step  2303  subtracts only a part quantity equal to the quantity of parts to be warehoused.  
      Then, step  2304  subtracts the quantity of parts to be warehoused (which is the quantity before the above subtraction at step  2303 ) from the required part quantity to produce a remaining required part quantity. The remaining required part quantity indicates the part quantity by which the required part quantity exceeds the quantity of parts to be warehoused. (for the target part type in the target time period).  
      Then, step  2305  checks whether the remaining required part quantity is larger than 0. If it is not larger than 0, the processing flow proceeds to step  2302 , and the required part quantity for the next time period is subtracted. If the remaining required part quantity is larger than 0, on the other hand, the processing flow proceeds to step  2306 .  
      Step  2306  determines whether the target time period in which parts are needed is the time period t 1 . If it is determined that the target time period is the time period t 1 , the processing flow proceeds to step  2309 . If it is determined that the target time period is not the time period t 1 , on the other hand, the processing flow proceeds to step  2307 .  
      Step  2307  moves back the target time period to the previous time period (for the remaining required part quantity). For example, if the required part quantity is larger than the quantity of parts to be warehoused in the time period t 5 , the processing flow proceeds to a step at which the remaining required part quantity is subtracted from the quantity of parts to be warehoused in the time period t 4 . Then, step  2308  newly sets the remaining required part quantity as the required part quantity, and the processing flow proceeds to step  2309 .  
      Step  2309  determines whether steps  2303  through  2308  have been repeated for all time periods of the schedule to process the required part quantities. If it is determined that the steps have not yet been repeated for all time periods to process the required part quantities, the processing flow returns to step  2302 . If it is determined that the steps have been repeated for all time periods to process the required part quantities, the processing flow proceeds to step  2310 .  
      Step  2310  determines whether steps  2302  through  2309  have been repeated for all part types. If it is determined that the steps have not yet been repeated for all part types, the processing flow returns to  2301 . If it is determined that the steps have been repeated for all part types, the processing flow proceeds to step  2311 .  
      Step  2311  sets as an overstocked parts quantity the quantity of parts to be warehoused for each time period from which any required part quantity have not been subtracted (or, for the time period t 1 , the sum of the inventory up to that time period and the quantity of parts to be warehoused for that time period), and the processing flow ends.  
      As described above, steps  2303  through  2308  are repeated so as to subtract each required part quantity from the quantity of parts to be warehoused in the corresponding time period and thereby calculate the quantity of parts to be warehoused which are not be used for a current model, that is, the (quantity of) overstocked parts to be warehoused.  
       FIG. 26  shows the details of step  1603 . This example shows a method for calculating the number of products which can be produced (producible product quantity) for each model. First of all, step  2501  starts a loop consisting of the subsequent steps  2502  through  2515  to be repeated for each retired model.  
      Step  2502  estimates the inventory schedule of each part type based on the above current parts inventory and the parts delivery schedule. The inventory schedule is obtained by adding the quantity of parts to be warehoused to the current part inventory over all time periods.  FIG. 27  shows an example of this estimation.  FIG. 27 ( a ) shows the inventory quantity of the part c 106 . Specifically, the horizontal axis indicates each time period of the schedule, while the vertical axis indicates the inventory quantity, taking into no account the quantity of the parts to be warehoused or retrieved. In  FIG. 27 ( b ), the horizontal axis indicates each time period of the schedule, while the vertical axis indicates the quantity of the parts c 1706  to be warehoused. Specifically,  FIG. 27 ( b ) indicates that parts will be warehoused in the time periods t 1 , t 6 , and t 11 . In  FIG. 27 ( c ), the horizontal axis indicates each time period of the schedule, while the vertical axis indicates the estimated inventory quantity of the parts c 1706  including the quantity of the parts to be warehoused shown in  FIG. 27 ( b ).  
      Then, step  2503  starts a loop consisting of the subsequent steps  2504  through  2514  to be repeated for each time period of the production schedule. The length of each time period for which the loop is repeated can be freely set by the operator. Then, step  2504  sets the initial planned product quantity to ∞. After that, step  2505  explodes a target model (product) into required part quantities based on the above information on a bill of materials.  
      Then, step  2506  starts a loop consisting of the subsequent steps  2507  through  2512  to be repeated for each component part type. Step  2507  determines whether the above exploded required part quantity for each component part type is larger than the estimated part inventory quantity for that component part type. If it is determined at step  2507  that the required part quantity is larger than the estimated part inventory quantity, the processing flow proceeds to step  2508 . If it is determined that the required part quantity is not larger than the estimated part inventory quantity, on the other hand, the processing flow proceeds to step  2510 .  
      Step  2508  checks whether parts of a target part type can be delivered in time if the order is newly issued at this time point. If the parts can be delivered in time, the processing flow proceeds to step  2509 .  
      If the parts cannot be delivered in time, on the other hand, the processing flow proceeds to step  2510 . Step  2509  sets the quantity of parts of the target part type which can be procured to be equal to the required part quantity. Step  2510  sets the quantity of parts of the target part type which can be procured to be equal to the estimated part inventory quantity. Both steps  2509  and  2510  proceed to step  2511 .  
      Step  2511  divides the procurable part quantity for the target part type by the number of parts of that part type constituting each product to obtain a part-basis producible product quantity for the target part type. Then, step  2512  updates the part inventory schedule for all time periods after this time period. Specifically, step  2512  subtracts the estimated part inventory for this time period from the estimated part inventory for each time period after this time period and sets the result as the updated estimated part inventory for a respective time period.  
      Step  2513  determines whether the loop consisting of steps  2507  through  2512  has been repeated for all component part types. If it is determined that the loop consisting of steps  2507  through  2512  has been repeated for all component part types, the processing flow proceeds to step  2514 . If it is determined that the loop has not yet been repeated for all component part types, on the other hand, the processing flow returns to step  2506 . Step  2514  selects the minimum value from among the part-basis producible product quantities as the producible product quantity.  
      Then, step  2515  determines whether the loop consisting of steps  2504  through  2514  has been repeated for all time periods of the production schedule. If it is determined that the loop consisting of steps  2504  through  2514  has been repeated for all time periods of the production schedule, the processing flow proceeds to step  2516 . If it is determined that the loop has not yet been repeated for all time periods of the production schedule, on the other hand, the processing flow returns to step  2503 .  
      Step  2516  determines whether the loop consisting of steps  2502  through  2515  has been repeated for all retired models. If it is determined that the loop consisting of steps  2502  through  2515  has been repeated for all retired models, the processing flow ends. If it is determined that the loop has not yet been repeated for all retired models, on the other hand, the processing flow returns to step  2501 .  
      As described above, by carrying out calculations for each model and each time period, it is possible to calculate the producible product quantity for each model in the case where all overstocked parts are assigned to the model. It should be noted that in addition to the above method in which a producible product quantity is calculated for each model, it is possible to employ a “priority-model-basis producible product quantity calculating” method which performs the steps of: giving priority to each retired model; calculating the producible product quantity for the retired model having the highest priority; and calculating the producible product quantity for the retired model having the second highest priority by use of the remaining parts (and so on). Furthermore, the producible product quantity for each retired model can be determined by using as an evaluation criterion an additional parts order quantity or gain and loss (described later) and employing a gradient method or a linear programming method such that the item selected as the evaluation criterion has a best value.  
       FIG. 28  shows the details of step  1604 . First, step  2601  calculates the value of an additional parts order. This step is performed by the additional parts order estimating section  1518 .  FIG. 29  shows the details of the calculation method.  
      First of all, step  2701  starts a loop consisting of the subsequent steps  2702  through  2713  to be repeated for all models. Step  2702  starts a loop consisting of the subsequent steps  2703  through  2711  to be repeated for every production quantity starting from 0 up to the producible product quantity calculated at step  1603 . Step  2703  explodes a target production quantity of products into required part quantities based on the information on a bill of materials. Step  2704  starts a loop consisting of the subsequent steps  2705  through  2710  to be repeated for all component part types.  
      Step  2705  determines whether the required part quantity for a target component part type is larger than the (corresponding) estimated parts inventory quantity. If it is determined that the required part quantity for the target component part type is larger than the estimated parts inventory quantity, the processing flow proceeds to step  2706 . If it is determined that the required part quantity for the target component part type is not larger than the estimated parts inventory quantity, on the other hand, the processing flow proceeds to step  2708 .  
      Step  2706  checks whether parts of the target part type can be delivered in time if the order is issued at this time point, that is, whether a new order for parts of the target part type can be placed. If the new order can be placed, the processing flow proceeds to step  2707 . If the new order cannot be placed, on the other hand, the processing flow proceeds to step  2708 . Step  2707  sets the additional order quantity to be equal to the required part quantity for the target part type minus the estimated part inventory quantity, and the processing flow proceeds to step  2709 . Step  2708  sets the additional order quantity to 0, and the processing flow proceeds to step  2709 .  
      Step  2709  calculates the value of the additional order for the target part type based on the additional (parts) order quantity. The value of the additional (parts) order is obtained by multiplying the additional order quantity by the purchasing price of the target part type. Then, step  2710  adds the value of the additional order for the target part type to the value of the additional parts order (total additional order) so that after the loop has been repeated for all component part types, the value of the additional parts order (total additional order) for each production quantity can be obtained.  
      Then, step  2711  determines whether the loop consisting of steps  2705  through  2710  has been repeated for all component part types. If it is determined that the loop has been repeated for all component part types, the processing flow proceeds to step  2712 . If it is determined that the loop has not yet been repeated for all component part types, on the other hand, the processing flow returns to step  2704 .  
      Step  2712  determines whether the loop consisting of steps  2703  through  2711  has been repeated for all possible production quantities. If it is determined that the loop has been repeated for all possible production quantities, the processing flow proceeds to step  2713 . If it is determined that the loop has not yet been repeated for all possible production quantities, the processing flow returns to step  2702 .  
      Step  2713  determines whether the loop consisting of steps  2702  through  2712  has been repeated for all models. If it is determined that the loop has been repeated for all models, the processing flow ends. If it is determined that the loop has not yet been repeated for all models, on the other hand, the processing flow returns to step  2701 . A result from the above processing is shown in  FIG. 30 . In the figure, the horizontal axis indicates the production quantity, while the vertical axis indicates the value of the additional parts order.  
      Then, step  2602  calculates the estimated sales amount for each retired model.  
      This step is carried out by the above retired model sales amount calculating section  1519 . Specifically, the retired model sale amount calculating section  1519  multiplies the above producible product quantity (for each retired model) by the above product selling price (information) for each time period shown in  FIG. 21 ( b ).  
      Then, step  2603  calculates the estimated parts sales amount. This step is carried out by the above retired parts selling schedule estimating section  1522 . Specifically, the retired parts selling schedule estimating section  1522  performs the steps of: calculating the required part quantity for the producible product quantity (for each model) based on the producible product quantity and the above information on a bill of materials; subtracting the required part quantity for the producible product quantity from the above overstocked parts (quantity) to obtain the post-production overstocked parts (quantity); comparing the post-production overstocked parts (quantity) with the above sellable parts information shown in  FIG. 22 ( c ); if the surplus part quantity is larger than the sellable part quantity, setting the sellable part quantity of parts (of the target part type) as sellable; and if the surplus part quantity is not larger than the sellable part quantity, setting the post-production surplus part quantity of parts (of the target part type) as sellable. The above newly-set sellable part quantity is multiplied by the (corresponding) parts selling price included in the above parts selling price information to obtain the estimated parts sales amount. Furthermore, the retired parts selling schedule estimating section  1522  subtracts the sellable (part) quantity from the post-production surplus part (quantity) to obtain the post-sale overstocked parts (quantity). It should be noted that by setting a value of 0 for the sellable part quantity in  FIG. 22 ( c ), it is possible to evaluate a case in which parts are not sold.  
      Then, step  2604  calculates the additional manufacturing cost. This step is carried out by the additional manufacturing cost calculating section  1523 . Specifically, the additional manufacturing cost calculating section  1523  multiplies the above producible product quantity by the above manufacturing cost (information) shown in  FIG. 22 ( d ). It should be noted, however, that if the production capability of the production line for the target products are fixed and furthermore the total production quantity does not increase even when the production quantity for each model is changed, the production line cost can be regarded as fixed. Accordingly, the manufacturing cost can be assumed to be zero, and the above manufacturing cost information may be set as such. An example in which the production capability of the production line is fixed is that production is scheduled to be carried out by 10,000 workers for 8 hours per day (that is, the production line has the corresponding production capability) and the wages for them are predetermined to be paid without fail.  
      Then, step  2605  calculates the profit and loss. This step is carried out by the retired parts disposal section  1520 . This step calculates the profit and loss for each model based on the above retired model sales amount, estimated parts sales amount, additional parts order value, additional manufacturing cost, and post-sale overstocked parts (quantity) using the following formula (Formula 1). At that time, the production quantity and the part sales quantity are changed within the above producible product quantity and the above sellable part quantity, respectively. 
 
profit or loss=retired model sales amount+estimated parts sales amount−additional parts order value−additional manufacturing cost−post-sale overstocked parts (quantity)×parts selling price  (Formula 1) 
 
      The above profit or loss is the output from step  1604 .  FIG. 31  shows this output. In the figure, the horizontal axis indicates the production quantity, while the vertical axis indicates the calculation result of the formula (Formula 1) for each production quantity, that is, the profit or loss.  
      Then, step  1605  determines a quantity to be added to the planned production quantity and a quantity to be added to the quantity of parts to be sold based on the above profit and loss for each model obtained at step  1604 . This determination may be made by the operator interactively with the above operator input/output apparatus  1502 . Or alternatively, the above retired parts disposal section  1520  may determine a production quantity and a part sales quantity at which the profit is maximized (loss is minimized) based on the above the profit and loss for each model. An example of the determination made interactively by the operator will be described later. The determined planned production quantity and part sales quantity are supplied to step  1606 . Step  1606  determines whether any addition has been made to the planned production quantity at step  1605 . If it is determined that some addition has been made to the planned production quantity, the processing flow returns to step  1602 . If it is determined that no addition has been made to the planned production quantity, on the other hand, the processing flow ends. Step  1602  performs the steps of: when overstocked parts are estimated, exploding a quantity of products equal to the above quantity added to the planned production quantity at step  1605  based on the above information on a bill of materials; and subtracting the resultant additional production plan required-part quantity and the above part sales quantity from the surplus part quantity to obtain overstocked parts (quantity) left after the above additions to the production plan (planned production quantity) and the quantity of parts to be sold.  
      As described above, steps  1602  through  1606  are repeated, and then evaluation is made based on the profit and loss calculated at step  1604  to determine a retired model production plan and the quantity of parts to be sold (for each part type). With this arrangement, it is possible to dispose of the retired parts inventory and retired parts to be warehoused with minimum loss.  
      Description will be made below of an example in which the operator (planner) interactively drafts a production plan for a retired model with reference to  FIGS. 32 and 33 .  
       FIG. 32  shows interactive screens used when no parts are sold. First, a producible product quantity calculation results screen  3101  is displayed to the planner. This screen indicates the producible product quantity for each model in each time period and the value of the corresponding additional (parts) order. On the screen, the planner selects a model whose production plan is to be drafted by comparing the selling prices of models to one another. If the operator (planner) selects a field of a target model by use of a mouse or a keyboard and further selects an Add Plan button  3104  by use of a mouse or a keyboard, the producible product quantity for the target model in each time period and the value of the corresponding additional (parts) order are copied to an additional production plan input screen  3102 .  
      On the additional production plan input screen  3102 , the field to which the producible product quantity and the value of the corresponding additional parts order are copied is referred to as an additional production plan field. On the additional production plan input screen  3102 , as an additional production plan, the planner enters a value, which is smaller than a respective producible product quantity, in the additional production plan field of each model for each time period by use of a mouse or a keyboard. When determining the value, if the planner selects the additional production plan field of a target model for a target time period by use of a mouse or a keyboard and further selects a Detail button  3105  by use of a mouse or a keyboard, a detailed parts information screen  3103  is displayed.  
      The detailed parts information screen  3103  displays, for each (possible) production quantity, the names of parts to be additionally ordered for the target model in the target time period and the value of the order. The planner checks each production quantity, the names of parts to be additionally ordered, the value of the order, and the selling price of the product, and selects a desired product production quantity by use of a mouse or a keyboard. After selecting the desired product production quantity, if the planner selects an Enter button  3108  by use of a mouse or a keyboard, the selected production quantity (for the production plan) is copied to the production quantity field of the target model for the target time period on the additional production plan input screen  3102 . On the other hand, if the planner does not want to produce any products of the target model in the target and subsequent time periods, the planner selects the production quantity field of the target model for the target time period on the additional production plan input screen  3102  by use of a mouse or a keyboard and further selects a “No Production For Subsequent Time Periods” button  3106  by use of a mouse or a keyboard to set a value of 0 for the production quantity fields of the target model for the target time period and all the subsequent time periods on the additional production plan input screen  3102 .  
      After drafting a final retired model production plan by repeating the above operation for each model, the planner selects an Enter Plan button  3107  on the additional production plan input screen  3102  by use of a mouse or a keyboard to decide an additional production plan for each retired model.  
       FIG. 33  shows interactive screens used when parts are sold. The producible product quantity calculation results screen  3201  corresponds to the producible product quantity calculation results screen  3101 ; the additional production plan input screen  3202  corresponds to the additional production plan input screen  3102 ; and the detailed parts information screen  3203  corresponds to the detailed parts information screen  3103 . These screens shown in  FIG. 33  are different from those shown in  FIG. 32  in that they each indicate parts sales income to the planner. The planner first refers to the producible product quantity calculation results screen  3201 , and checks the relationship between the producible product quantity and the value of the additional order for each model and the parts sales income earned when no production is carried out to select a model whose production plan is to be determined. The producible product quantity for the target model in each time period is copied to the additional production plan input screen  3202  by carrying out the same operation as that indicated by  FIG. 32 . As shown in  FIG. 33 , selecting a Detail button  3205  on the additional production plan input screen  3202  displays the detailed parts information screen  3203  which displays two tables to the planner: one including fields indicating production quantities, the names of parts to be additionally ordered, and the values of additional orders; and the other including fields indicating production quantities, the names of parts to be sold, and the sales amounts.  
      With this arrangement, the planner can aim to draft a production plan for a retired model in which the profit is maximized (or loss is minimized) based on the values of additional orders, the parts sales income, and the product selling price.  
      Description will be made below of a variation of the above example described with reference to FIGS.  17  to  33 . In this example, no production plan (information) has been promised to the outside, and therefore it can be assumed that all models to be produced are retired models. In such a case, both the required parts explosion processing at step  1601  and the overstocked parts-extraction processing at step  1602  shown in  FIG. 18  may be omitted. The retired parts estimating section  1516  may set both the parts inventory information stored in the parts inventory information storage section  1506  and the parts delivery schedule stored in the parts delivery schedule storage section  1507  as information on parts used for only retired models. Then, the producible product quantity calculating section  1517  may calculate the producible product quantity for each retired model.  
      Description will be made below of another variation of the above example described with reference to FIGS.  17  to  33 . In this example, a production plan (information) has been already promised to the outside, and therefore it is necessary to execute the production plan even if it is of a retired model. In such a case, in the required parts explosion processing at step  1601  shown in  FIG. 18 , the MRP explosion apparatus  1515  may treat the production plan of a retired model whose production has been already promised, as that of a current model.  
      Description will be made below of still another variation of the above example described with reference to FIGS.  17  to  33 . In this example, a production plan of a new model is stored as production planning information. In such a case, in the required parts explosion processing at step  1601  shown in  FIG. 18 , the MRP explosion apparatus  1515  may treat the production plan of a new model as that of a current model.  
       FIG. 34  shows an example of the product selling price determination algorithm according to the present invention. This algorithm determines the product selling price information stored in the product selling price information storage section  1510 . Of the steps in  FIG. 34 , steps  3001  to  3003  perform the same processing as that performed at steps  1601  to  1603  shown in  FIG. 18 , respectively. Specifically, based on a predetermined production plan, step  3001  explodes (a product into) required part quantities and step  3002  extracts overstocked parts based on the exploded required part quantities. Step  3003  calculates the producible product quantity for each retired model in each time period based on the overstocked parts extracted at step  3002 . Step  3004  calculates the minimum product selling pride for each model based on an estimated parts sales amount, an additional parts order value, an additional manufacturing cost, and (the quantity of) post-sale overstocked parts, using the following formula (Formula 2). At that time, the production quantity and the part sales quantity are changed within the above producible product quantity and sellable part quantity, respectively. This step ( 3004 ) is carried out by the product selling price calculating section  1521 . 
 minimum product selling price=(−estimated parts sales amount+additional parts order value+additional manufacturing cost+post-sale overstocked parts quantity×parts selling price)/planned production quantity  (Formula 2)  
      The above minimum product selling price is the output from step  3004 .  
       FIG. 35  shows the details of step  3004 . In the figure, steps  3501 ,  3502 , and  3503  perform the same processing as that performed at steps  2601 ,  2603 , and  2604  shown in  FIG. 28 , respectively. Specifically, step  3501  calculates the value of an additional parts order; step  3502  calculates an estimated parts sales amount; and step  3503  calculates an additional manufacturing cost. Then, step  3504  extracts post-sale overstocked parts, and step  3505  calculates the minimum product selling price for each model by use of Formula 2.  
      Then, step  3005  determines a product selling price based on the minimum product selling price. This determination may be made by the operator interactively with the above operator input/output apparatus  1502 . Or alternatively, the minimum product selling price may be set as the product selling price as it is. Since the determined product selling price of each model does not change with each time period, this constant value is exploded over all time periods of the schedule for each model. The product selling price thus exploded over all time periods of the schedule for each model is registered in the above product selling price information storage section  1510 . This product selling price is used to perform the production plan adjustment processing shown in  FIG. 18 , making it possible to draft a production plan for a retired model with a small loss. It should be noted that after a product selling price has been registered in the product selling price information storage section  1510 , the operator may set an estimated product selling price in the product selling price information storage section  1510  for each time period considering external conditions such as sales conditions. It should be further noted that if a satisfactory product selling price is not obtained for a model at step  3005 , the determination of the product selling price of the model may be suspended. In such a case, the product selling price determination algorithm may be executed later, or the operator may set an estimated product selling price of the model in the product selling price information storage section  1510  for each time period through the operator input/output apparatus  1502 .  
      Description will be made below of a variation of the above example described with reference to  FIGS. 34 and 35 . In this example, no production plan (information) has been promised to the outside, and therefore it can be assumed that all models to be produced are retired models. In such a case, both the required parts explosion processing at step  3001  and the overstocked parts extraction processing at step  3002  shown in  FIG. 34  may be omitted. Instead, the retired parts estimating section  1516  may set both the parts inventory information stored in the parts inventory information storage section  1506  and the parts delivery schedule-stored in the parts delivery schedule storage section  1507  as information on parts used for only retired models. Then, the producible product quantity calculating section  1517  may calculate the producible product quantity for each retired model.  
      Description will be made below of another variation of the above example described with reference to  FIGS. 34 and 35 . In this example, a production plan (information) has been already promised to the outside, and therefore it is necessary to execute the production plan even if it is of a retired model. In such a case, in the required parts explosion processing at step  3001  shown in  FIG. 34 , the MRP explosion apparatus  1515  may treat the production plan of a retired model whose production has been already promised, as that of a current model.  
      Description will be made below of still another variation of the above example described with reference to  FIGS. 34 and 35 . In this example, a production plan of a new model is stored as production planning information. In such a case, in the required parts explosion processing at step  3001  shown in  FIG. 34 , the MRP explosion apparatus  1515  may treat the production plan of a new model as that of a current model.  
       FIG. 36  shows the hardware configuration of the master production scheduling system  1500  shown in  FIG. 17 .  
      In the figure, a computer  3600  comprises: a bus  3601 ; a main unit  3602  connected to the bus  3601 ; an external storage apparatus  3603  connected to the bus  3601 ; an input apparatus  3604  connected to the bus  3601 ; and an output apparatus  3605  connected to the bus  3601 . The main unit  3602  includes a main storage unit  36021  and a CPU (Central Processing Unit)  36022 .  
      In the computer  3600 , the main storage unit  36021  stores various programs and data necessary to execute these programs. The CPU  36022  executes a program stored in the main storage  36021  using data stored in the main storage  36021 . The external storage apparatus  3603  may have a capacity larger than that of the main storage unit  36021 . Programs and data to be stored in the main storage unit  36021  may be stored in the external storage apparatus  3603 , and then read out from the external storage apparatus  3603  into the main storage unit  36021  by the CPU  36022  as necessary. As the external storage apparatus  3603 , it is possible to use a floppy disk, which is a portable medium, a CD-ROM (Compact Disk Read-Only Memory), etc. in addition to a hard disk device.  
      In the computer  3600 , the input apparatus  3604  is made up of an input control section (not shown) and an input section (not shown), such as a mouse or a keyboard, connected to the input control section. The input apparatus  3604  receives information entered by the operator by use of the input section such as a mouse or a keyboard. The output apparatus  3605  is made up of an output control section (not shown) and an output section (not shown), such as a display or a printer, connected to the output control section. The output apparatus  3605  can output to the output section, such as a display or a printer, data read from the external storage apparatus  3603  into the main storage unit  36021  by the CPU  36022 . The output apparatus  3605  also can output a program execution result by the CPU  36022  to the output section such as a display or a printer.  
      Each apparatus in  FIG. 17  described above is implemented by the components in  FIG. 36  as follows.  
      The external storage apparatus  3603  realizes a function of the following sections in the data storage apparatus  1501  to permanently store temporarily-held information: the production planning information storage section  1504 , the information on a bill of materials storage section  1505 , the parts inventory information storage section  1506 , the parts delivery schedule storage section  1507 , the parts purchasing price information storage section  1508 , the retired model information storage section  1509 ′, the product selling price information storage section  1510 , the sellable product quantity information storage section  1511 , the parts selling price information storage section  1512 , the sellable parts information storage section  1513 , and the manufacturing cost information storage section  1514 . The main storage unit  36021 , on the other hand, realizes another function of the above sections in which the operator refers to or updates stored information, or the operator registers new information.  
      The MRP explosion apparatus  1515  and the retired parts estimating section  1516 , the producible product quantity calculating section  1517 , the additional parts order estimating section  1518 , the retired model sales amount calculating section  1519 , the retired parts disposal section  1520 , the product selling price calculating section  1521 , the retired parts selling schedule estimating section  1522 , and the additional manufacturing cost calculating section  1523  all included in the “retired model overstocked parts disposal method determining” apparatus  1503  are implemented by performing the steps of: storing into the external storage apparatus  3603  programs designed to carry out the operations of the above apparatuses and sections; reading these programs from the external storage apparatus  3603  into the main storage unit  36021 ; and executing the programs by use of the CPU  36022 . When interactively drafting a production plan of a retired model, the operator can enter an instruction from the input apparatus  3604  while displaying the display screens as shown in  FIGS. 32 and 33  in the output apparatus  3605  so that the production plan is drafted based on the entered instruction.  
      The operator input/output apparatus  1502  is implemented by the input apparatus  3604  and the output apparatus  3605 .  
      It should be noted that the following hardware configuration, which is a variation of the above hardware configuration, may be employed. A plurality of computers are connected to one another such that they can exchange data. With this arrangement, the MRP explosion apparatus  1515  and the “retired model overstocked parts disposal method determining” apparatus  1503  may be each implemented by a separate computer.  
      According to the present invention, a master production scheduling system comprises a “retired model overstocked parts disposal method determining” apparatus, performing the steps of: extracting overstocked parts; calculating a producible product quantity for a retired model based on the overstocked parts; for each possible production quantity within the producible product quantity, calculating a sales amount, parts sales income to be earned from sales of parts left after the production, the value of an additional parts order, an additional manufacturing cost, and an inventory value for unsold parts; and selecting one of three options (measures) such as (1) produce products (utilizing the overstocked parts) and make efforts to increase the sales, (2) sell the overstocked parts as they are, and (3) abandon the overstocked parts as they are; wherein when one of the above measures is executed, it is possible to prevent loss from increasing by evaluating beforehand the profit and loss based on the sales amount, the parts sales income, the value of the additional parts order, the additional manufacturing cost, and the inventory value.  
     Industrial Usability  
      A master production scheduling system according to the present invention comprises a “retired model overstocked parts disposal method determining” means and is capable of determining a method for disposing of overstocked parts with minimum loss, making it possible to improve corporate financial measures.