Clingcon: The next generation

Abstract

AbstractWe present the third generation of the constraint answer set systemclingcon, combining Answer Set Programming (ASP) with finite domain constraint processing (CP). While its predecessors rely on a black-box approach to hybrid solving by integrating the CP solvergecode, the newclingconsystem pursues a lazy approach using dedicated constraint propagators to extend propagation in the underlying ASP solverclasp. No extension is needed for parsing and groundingclingcon's hybrid modeling language since both can be accommodated by the new generic theory handling capabilities of the ASP groundergringo. As a whole,clingcon3 is thus an extension of the ASP systemclingo5, which itself relies on the groundergringoand the solverclasp. The new approach ofclingconoffers a seamless integration of CP propagation into ASP solving that benefits from the whole spectrum ofclasp's reasoning modes, including, for instance, multi-shot solving and advanced optimization techniques. This is accomplished by a lazy approach that unfolds the representation of constraints and adds it to that of the logic program only when needed. Although the unfolding is usually dictated by the constraint propagators during solving, it can already be partially (or even totally) done during preprocessing. Moreover,clingcon's constraint preprocessing and propagation incorporate several well-established CP techniques that greatly improve its performance. We demonstrate this via an extensive empirical evaluation contrasting, first, the various techniques in the context of CSP solving and, second, the newclingconsystem with other hybrid ASP systems.