Debugging Inconsistent Answer Set Programs

In this paper we examine how we can find contradictions from Answer Set Programs (ASP). One of the most important phases of programming is debugging, finding errors that have crept in during program implementation. Current ASP systems are still mostly experimental tools and their support for debugging is limited. This paper addresses one part of ASP debugging, finding the reason why a program does not have any answer sets at all. The basic idea is to compute diagnoses that are minimal sets of constraints whose removal returns consistency. We compute also conflict sets that are sets of mutually incompatible constraints. The final possible source of inconsistency in an ASP program comes from odd negative loops and we show how these may also be detected. We have created a prototype for the ASP debugger that is itself implemented using ASP.