A method and apparatus for computer modeling the production process is disclosed. An integrated product and process engineering system may be a computer modeling system that models both a generic production process and a specific individual production process. The integrated product and process engineering system may store one or more time dependent process parameters related to the production process and one or more engineering change numbers related to different product designs. The effective time periods of the time dependent process parameters may be compared with the effective time periods of the engineering change numbers. Various flags may be associated with each comparison to indicate the validity of the time dependent process parameter.