“…Others include Object-Oriented Database Systems such as GemStone (Bretl, Otis et al, 1989) and O 2 (Bancilhon, Barbedette et al, 1988), which have at their core a persistent object store, and process modelling systems, which use a persistent base to preserve their modelling activities over execution sessions (Bruynooghe, Parker et al, 1991;Curtis, Kellner et al, 1992;Han and Welsh, 1993). Some persistent programming systems allow software engineering environments to be completely supported within the persistent system (Currie, 1985;Bretl, Otis et al, 1989;Morrison, Brown et al, 1994).…”