“…There are many theoretical papers that deal with the problem of implementation ( [Bol and Degerstedt, 1993;Kemp et al, 1991;Degerstedt and Nilsson, 1995;Fernández et al, 1993]) but only few running systems. The problem of handling and representing ground programs given a non-ground one has also been adressed [Kagan et al, 1994;Kagan et al, 1995;Eiter et al, 1997a].…”