The data processing system has an online transactional processing (OLTP) system for receiving of reporting data from work centers of a production line. The production line is logically divided into shop areas. At the exits of each shop area where an intermediate product is completed one reporting point serves as exit point in order to report the completion of an intermediate production step. This data is stored in the OLTP system and retrieved at a later point of time in order to generate a table containing aggregated intermediate product quantities per shop area. This table is transferred to a financial data server for calculation of the value of work in progress.