Improving MCS Enumeration via Caching

Enumeration of minimal correction sets (MCSes) of conjunctive normal form formulas is a central and highly intractable problem in infeasibility analysis of constraint systems. Often complete enumeration of MCSes is impossible due to both high computational cost and worst-case exponential number of MCSes. In such cases partial enumeration is sought for, finding applications in various domains, including axiom pinpointing in description logics among others. In this work we propose caching as a means of further improving the practical efficiency of current MCS enumeration approaches, and show the potential of caching via an empirical evaluation.Peer reviewe

Incrementally Computing Minimal Unsatisfiable Cores of QBFs via a Clause Group Solver API

We consider the incremental computation of minimal unsatisfiable cores (MUCs) of QBFs. To this end, we equipped our incremental QBF solver DepQBF with a novel API to allow for incremental solving based on clause groups. A clause group is a set of clauses which is incrementally added to or removed from a previously solved QBF. Our implementation of the novel API is related to incremental SAT solving based on selector variables and assumptions. However, the API entirely hides selector variables and assumptions from the user, which facilitates the integration of DepQBF in other tools. We present implementation details and, for the first time, report on experiments related to the computation of MUCs of QBFs using DepQBF's novel clause group API.Comment: (fixed typo), camera-ready version, 6-page tool paper, to appear in proceedings of SAT 2015, LNCS, Springe

Dealing Automatically with Exceptions by Introducing Specificity in ASP

Answer Set Programming (ASP), via normal logic programs, is known as a suitable framework for default reasoning since it offers both a valid formal model and operational systems. However, in front of a real world knowledge representation problem, it is not easy to represent information in this framework. That is why the present article proposed to deal with this issue by generating in an automatic way the suitable normal logic program from a compact representation of the information. This is done by using a method, based on specificity, that has been developed for default logic and which is adapted here to ASP both in theoretical and practical points of view

Finding graph decompositions via SAT

We begin a systematic study of how Graph Decomposition problems may be represented using propositional formulas, and hence solved using SAT-solver technology. By making use of symmetry breaking techniques we are able to obtain solutions to several previously unknown cases and to significantly reduce the time needed to compute decompositions. However some fairly small instances remain unsolved, and thus provide an interesting challenge to SAT-solver technology

Finding graph decompositions via SAT

We begin a systematic study of how Graph Decomposition problems may be represented using propositional formulas, and hence solved using SAT-solver technology. By making use of symmetry breaking techniques we are able to obtain solutions to several previously unknown cases and to significantly reduce the time needed to compute decompositions. However some fairly small instances remain unsolved, and thus provide an interesting challenge to SAT-solver technology

On Computing the Union of MUSes

The situation is considered where a satisfiability problem represents for example a manufacturing specification, and thus unsatisfiability of the problem means that something is wrong with the specification. In response to this an infeasibility analysis is needed, where we consider the robust notion of "union of MUSes", that is, all clauses need to be computed, which are potentially necessary for the contradiction to arise (become necessary after some some other clauses are removed).The paper proposes a novel algorithm for this problem, proves its correctness, and provides experimental evidence for practical applicability

A General Artificial Intelligence Approach for Skeptical Reasoning

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