1. A data processing system implemented method of extending specifications of a process model within a workflow process environment, wherein said process model defines a process activity managed and executed by at least one data processing system and said process activity has associated with it an interface container implemented within a reusable parts environment, said method comprising the steps of: linking said process model with said reusable parts environment; associating with said process model, an interface container reusable part, said interface container reusable part implementing said interface container and residing within said reusable parts environment; and storing an interface container reusable part specification corresponding to said interface container reusable part within said process model such that said specifications of said process model are extended in response to said associating step.