Characterizing ASP Inferences by Unit Propagation

Computational approaches to Satisfiability Checking (SAT) and Answer Set Programming (ASP) have many aspects in common. In fact, the basic algorithms of ASP solvers are very similar to the Davis-Logemann-Loveland procedure (DLL) for SAT. The major difference lies in the inference rules, which are more complex in ASP. In this paper, we provide a generic framework, based on concepts from Constraint Processing (CSP), which allows us to view ASP inferences as forms of unit propagation. We develop declarative characterizations of ASP solvers nomore++ and smodels in terms of constraints. By putting ASP solving into a common context with SAT and CSP, we shed new light on ASP solving techniques and their relationships to neighboring fields.