On forgetting postulates in answer set programming
Jianmin Ji, Jia-Huai You, Yisong Wang · 2015
Forgetting is an important mechanism for logic-based agent systems. A recent interest has been in the desirable properties of forgetting in answer set programming (ASP) and their impact on the design of forgetting operators. It is known that some sub-sets of these properties are incompatible, i.e., they cannot be satisfied at the same time. In this paper, we are interested in the question on the largest set ∆ of pairs (Π, V), where Π is a logic program and V is a set of atoms, such that a forgetting operator ex-ists that satisfies all the desirable properties for each (Π, V) in ∆. We answer this question positively by discovering the precise condition under which the knowledge forgetting, a well-established approach to forgetting in ASP, satisfies the property of strong persistence, which leads to a sufficient and neces-sary condition for a forgetting operator to satisfy all the desirable properties proposed in the literature. We explore computational complexities on check-ing the condition and present a syntactic character-ization which can serve as the basis of computing knowledge forgetting in ASP.