This paper addresses the issues related to the practice of modelling process data for computer aided concurrent engineering (CAGE) environment in the context of the development of a STEP (The Standard for the Exchange of Product Model Data) Application Protocol (AP). The requirements for the process data over the life cycle of process plant are identified and emphasise sharability, reusability, and interoperability of data models. The approach follows the EPISTLE (European Process Industries STEP Technical Liaison Executive) framework and Core model to develop a process data model. Subsequent analysis provides a basis for evaluation of the benefits of such models in which some extensions suggest to the EPISTLE data modelling methodology.