Christian Anger

The nomore ++ approach to answer set solving

We present a new answer set solver, called nomore++, along with its underlying theoretical foundations. A distinguishing feature is that it treats heads and bodies equitably as computational objects. Apart from its operational foundations, we show how it improves on previous work through its new lookahead and its computational strategy of maintaining unfounded-freeness. We underpin our claims by selected experimental results.

NoMoRe: A System for Non-Monotonic Reasoning under Answer Set Semantics

NoMoRe implements answer set semantics for normal logic programs. It realizes a novel paradigm to compute answer sets by computing a-colorings (non-standard graph colorings with two colors) of the block graph (a labeled digraph) associated with a given program P (see [5] for details). Intuitively, an a-coloring reflects the set of generating rules for an answer set, which means that noMoRe is rule-based and not atom-based like most of the other known systems. Since the core system was designed for propositional programs only, we have integrated lparse [8] as a grounder in order to deal with variables. Furthermore, we have included an interface to the graph drawing tool DaVinci [6] for visualization of block graphs. This allows for a structural analysis of programs.

NoMoRe: Non-monotonic Reasoning with Logic Programs

The non-monotonic reasoning system noMoRe [2] implements answer set semantics for normal logic programs. It realizes a novel, rule-based paradigm to compute answer sets by computing non-standard graph colorings of the block graph associated with a given logic program (see [8],[9],[6] for details). These non-standard graph colorings are called a-colorings or application-colorings since they reflect the set of generating rules (applied rules) for an answer set. Hence noMoRe is rule-based and not atom-based like most of the other known systems. In the recent release of noMoRe we have added backward propagation of partial a-colorings and a technique called jumping in order to ensure full (backward) propagation [6]. Both techniques improve the search space pruning of noMoRe. Furthermore, we have extended the syntax by integrity, weight and cardinality constraints [11],[5]1.

The nomore++ system

We present a new answer set solver nomore++. Distinguishing features include its treatment of heads and bodies equitably as computational objects and a new hybrid lookahead. nomore++ is close to being competitive with state-of-the-art answer set solvers, as demonstrated by selected experimental results.

Towards Systematic Benchmarking in Answer Set Programming: The Dagstuhl Initiative

Answer-set programming (ASP) emerged in the late 90s as a new logic programming paradigm [3,4,5], having its roots in nonmonotonic reasoning, deductive databases and logic programming with negation as failure. Since its inception, it has been regarded as the computational embodiment of nonmonotonic reasoning and a primary candidate for an effective knowledge representation tool. This view has been boosted by the emergence of highly efficient solvers for ASP [7,2]. It seems now hard to dispute that ASP brought new life to logic programming and nonmonotonic reasoning research and has become a major driving force for these two fields, helping dispell gloomy prophecies of their impending demise.

More on noMoRe

This paper focuses on the efficient computation of answer sets for normal logic programs. It concentrates on a recently proposed rule-based method (implemented in the noMoRe system) for computing answer sets. We show how noMoRe and its underlying method can be improved tremendously by extending the computation of deterministic consequences. With these changes noMoRe is able to deal with more challenging problem classes.

NoMoRe: A System for Non-monotonic Reasoning with Logic Programs under Answer Set Semantics

The noMoRe system (first prototype) implements answer set semantics for propositional normal logic programs. It uses an alternative implementation paradigm to compute answer sets by computing non-standard graph colorings of labeled directed graphs associated with logic programs. Therefore noMoRe is an interesting experimental tool for scientists working with logic programs on a theoretical or practical basis. Furthermore, we have included a tool for visualization of those graphs corresponding to programs.