WASP: A Native ASP Solver Based on Constraint Learning

Self Cite

Answer Set Programming (ASP) is a logic-based knowledge representation framework, supporting-among other reasoning modes-the central task of query answering. In the propositional case, query answering amounts to computing cautious consequences of the input program among the atoms in a given set of candidates, where a cautious consequence is an atom belonging to all stable models. Currently, the most efficient algorithms either iteratively verify the existence of a stable model of the input program extended with the complement of one candidate, where the candidate is heuristically selected, or introduce a clause enforcing the falsity of at least one candidate, so that the solver is free to choose which candidate to falsify at any time during the computation of a stable model. This paper introduces new algorithms for the computation of cautious consequences, with the aim of driving the solver to search for stable models discarding more candidates. Specifically, one of such algorithms enforces minimality on the set of true candidates, where different notions of minimality can be used, and another takes advantage of unsatisfiable cores computation. The algorithms are implemented in WASP, and experiments on benchmarks from the latest ASP competitions show that the new algorithms perform better than the state of the art. (Under consideration for acceptance in TPLP).

Section: Introductionmentioning

confidence: 99%

Cautious reasoning in ASP via minimal models and unsatisfiable cores

Alviano¹,

Dodaro²,

Järvisalo³

et al. 2018

Self Cite

“…The flurry of new research also led to the development of ELP solving systems (Kahl et al 2015;Son et al 2017). Such solvers employ readily available, highly efficient ASP systems like clingo Gebser et al 2014) and WASP (Alviano et al 2013), especially making use of the former solver's multi-shot solving functionality (Gebser et al 2019). However, these ELP solving systems rely on ground ASP programs when calling the ASP solver, which, for reasons rooted in complexity theory, generally requires multiple calls in order to check for world view existence.…”

Section: Examplementioning

confidence: 99%

selp: A Single-Shot Epistemic Logic Program Solver

Bichler¹,

Morak²,

Woltran³

2020

AbstractEpistemic logic programs (ELPs) are an extension of answer set programming (ASP) with epistemic operators that allow for a form of meta-reasoning, that is, reasoning over multiple possible worlds. Existing ELP solving approaches generally rely on making multiple calls to an ASP solver in order to evaluate the ELP. However, in this paper, we show that there also exists a direct translation from ELPs into non-ground ASP with bounded arity. The resulting ASP program can thus be solved in a single shot. We then implement this encoding method, using recently proposed techniques to handle large, non-ground ASP rules, into the prototype ELP solving system “selp,” which we present in this paper. This solver exhibits competitive performance on a set of ELP benchmark instances.

“…In this paper, we provide a practical contribution in the aforementioned context, in particular we present the external programming interface of the ASP solver WASP (Dodaro et al 2011;Alviano et al 2013;Alviano et al 2015), whose idea is to simplify the integration of custom heuristics and propagators in the solver. In particular, it offers multi-language support including python and perl languages that require no modifications to the solver, as well as C++ for performance-oriented implementations.…”

Section: Introductionmentioning

confidence: 99%

The External Interface for Extending WASP

Dodaro

Ricca

2018

Self Cite

Answer set programming (ASP) is a successful declarative formalism for knowledge representation and reasoning. The evaluation of ASP programs is nowadays based on the Conflict-Driven Clause Learning (CDCL) backtracking search algorithm. Recent work suggested that the performance of CDCL-based implementations can be considerably improved on specific benchmarks by extending their solving capabilities with custom heuristics and propagators. However, embedding such algorithms into existing systems requires expert knowledge of the internals of ASP implementations. The development of effective solver extensions can be made easier by providing suitable programming interfaces. In this paper, we present the interface for extending the CDCL-based ASP solver WASP. The interface is both general, i.e. it can be used for providing either new branching heuristics and propagators, and external, i.e. the implementation of new algorithms requires no internal modifications of WASP. Moreover, we review the applications of the interface witnessing it can be successfully used to extend WASP for solving effectively hard instances of both real-world and synthetic problems. Under consideration in Theory and Practice of Logic Programming (TPLP).