Computing Stable Models of Normal Logic Programs Without Grounding

Abstract: We present a method for computing stable models of normal logic programs, i.e., logic programs extended with negation, in the presence of predicates with arbitrary terms. Such programs need not have a finite grounding, so traditional methods do not apply. Our method relies on the use of a non-Herbrand universe, as well as coinduction, constructive negation and a number of other novel techniques. Using our method, a normal logic program with predicates can be executed directly under the stable model semantics without requiring it to be grounded either before or during execution and without requiring that its variables range over a finite domain. As a result, our method is quite general and supports the use of terms as arguments, including lists and complex data structures. A prototype implementation and non-trivial applications have been developed to demonstrate the feasibility of our method.