For any type of software to become standard, whether a third genera- tion language or an integrated project support environment (IPSE), it must undergo a series of modifications and updates which are a direct result of theoretical and empirical knowledge gained in the process. The database approach to the design of general purpose infonn- ation systems has undergone a series of revisions during the last twenty years which have established it as a winner in many different spheres of infonnation processing, including expert systems and real- time control. It is now widely recognised by...