Abstract: Computer implemented methods, data processing apparatus and manufacturing systems for determining or using current supplier schedule are described. A current customer requirement file is received including data items specifying a customer's current requirement of different parts each having associated supply dates from the supplier. The total quantity of each different type of part for each of a plurality of different time periods is determined. Data items specifying the total quantity of each different part and respective associated supply dates are stored in a current supplier schedule file. The current supplier schedule file is exported and can be displayed. A current net change in the supplier schedule based on the current supplier schedule and a previous supplier schedule can also be determined.