Result: Cooperating answer set programming

We present a formalism for logic program cooperation based on the answer set semantics. The system consists of independent logic programs that are connected via a sequential communication channel. When presented with an input set of literals from its predecessor, a logic program computes its output as an answer set of itself, enriched with the input. It turns out that the communication strategy makes the system quite expressive: essentially a sequence of a fixed number of programs n captures the complexity class ΣPn, i.e. the n-th level of the polynomial hierarchy. On the other hand, unbounded sequences capture the polynomial hierarchy PH. These results make the formalism suitable for complex applications such as hierarchical decision making and preference-based diagnosis on ordered theories. In addition such systems can be realized by implementing an appropriate control strategy on top of existing solvers such as DLV or SMODELS, possibly in a distributed environments.