TY - JOUR A1 - Mileo, Alessandra A1 - Schaub, Torsten H. A1 - Merico, Davide A1 - Bisiani, Roberto T1 - Knowledge-based multi-criteria optimization to support indoor positioning JF - Annals of mathematics and artificial intelligence N2 - Indoor position estimation constitutes a central task in home-based assisted living environments. Such environments often rely on a heterogeneous collection of low-cost sensors whose diversity and lack of precision has to be compensated by advanced techniques for localization and tracking. Although there are well established quantitative methods in robotics and neighboring fields for addressing these problems, they lack advanced knowledge representation and reasoning capacities. Such capabilities are not only useful in dealing with heterogeneous and incomplete information but moreover they allow for a better inclusion of semantic information and more general homecare and patient-related knowledge. We address this problem and investigate how state-of-the-art localization and tracking methods can be combined with Answer Set Programming, as a popular knowledge representation and reasoning formalism. We report upon a case-study and provide a first experimental evaluation of knowledge-based position estimation both in a simulated as well as in a real setting. KW - Knowledge representation KW - Answer Set Programming KW - Wireless Sensor Networks KW - Localization KW - Tracking Y1 - 2011 U6 - https://doi.org/10.1007/s10472-011-9241-2 SN - 1012-2443 SN - 1573-7470 VL - 62 IS - 3-4 SP - 345 EP - 370 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Durzinsky, Markus A1 - Marwan, Wolfgang A1 - Ostrowski, Max A1 - Schaub, Torsten H. A1 - Wagler, Annegret T1 - Automatic network reconstruction using ASP JF - Theory and practice of logic programming N2 - Building biological models by inferring functional dependencies from experimental data is an important issue in Molecular Biology. To relieve the biologist from this traditionally manual process, various approaches have been proposed to increase the degree of automation. However, available approaches often yield a single model only, rely on specific assumptions, and/or use dedicated, heuristic algorithms that are intolerant to changing circumstances or requirements in the view of the rapid progress made in Biotechnology. Our aim is to provide a declarative solution to the problem by appeal to Answer Set Programming (ASP) overcoming these difficulties. We build upon an existing approach to Automatic Network Reconstruction proposed by part of the authors. This approach has firm mathematical foundations and is well suited for ASP due to its combinatorial flavor providing a characterization of all models explaining a set of experiments. The usage of ASP has several benefits over the existing heuristic algorithms. First, it is declarative and thus transparent for biological experts. Second, it is elaboration tolerant and thus allows for an easy exploration and incorporation of biological constraints. Third, it allows for exploring the entire space of possible models. Finally, our approach offers an excellent performance, matching existing, special-purpose systems. Y1 - 2011 U6 - https://doi.org/10.1017/S1471068411000287 SN - 1471-0684 VL - 11 SP - 749 EP - 766 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Gebser, Martin A1 - Kaminski, Roland A1 - Schaub, Torsten H. T1 - Complex optimization in answer set programming JF - Theory and practice of logic programming N2 - Preference handling and optimization are indispensable means for addressing nontrivial applications in Answer Set Programming (ASP). However, their implementation becomes difficult whenever they bring about a significant increase in computational complexity. As a consequence, existing ASP systems do not offer complex optimization capacities, supporting, for instance, inclusion-based minimization or Pareto efficiency. Rather, such complex criteria are typically addressed by resorting to dedicated modeling techniques, like saturation. Unlike the ease of common ASP modeling, however, these techniques are rather involved and hardly usable by ASP laymen. We address this problem by developing a general implementation technique by means of meta-prpogramming, thus reusing existing ASP systems to capture various forms of qualitative preferences among answer sets. In this way, complex preferences and optimization capacities become readily available for ASP applications. KW - Answer Set Programming KW - Preference Handling KW - Complex optimization KW - Meta-Programming Y1 - 2011 U6 - https://doi.org/10.1017/S1471068411000329 SN - 1471-0684 VL - 11 IS - 3 SP - 821 EP - 839 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Gebser, Martin A1 - Kaufmann, Benjamin A1 - Schaub, Torsten H. T1 - Conflict-driven answer set solving: From theory to practice JF - Artificial intelligence N2 - We introduce an approach to computing answer sets of logic programs, based on concepts successfully applied in Satisfiability (SAT) checking. The idea is to view inferences in Answer Set Programming (ASP) as unit propagation on nogoods. This provides us with a uniform constraint-based framework capturing diverse inferences encountered in ASP solving. Moreover, our approach allows us to apply advanced solving techniques from the area of SAT. As a result, we present the first full-fledged algorithmic framework for native conflict-driven ASP solving. Our approach is implemented in the ASP solver clasp that has demonstrated its competitiveness and versatility by winning first places at various solver contests. KW - Answer set programming KW - Logic programming KW - Nonmonotonic reasoning Y1 - 2012 U6 - https://doi.org/10.1016/j.artint.2012.04.001 SN - 0004-3702 VL - 187 IS - 8 SP - 52 EP - 89 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Ostrowski, Max A1 - Schaub, Torsten H. T1 - ASP modulo CSP The clingcon system JF - Theory and practice of logic programming N2 - We present the hybrid ASP solver clingcon, combining the simple modeling language and the high performance Boolean solving capacities of Answer Set Programming (ASP) with techniques for using non-Boolean constraints from the area of Constraint Programming (CP). The new clingcon system features an extended syntax supporting global constraints and optimize statements for constraint variables. The major technical innovation improves the interaction between ASP and CP solver through elaborated learning techniques based on irreducible inconsistent sets. A broad empirical evaluation shows that these techniques yield a performance improvement of an order of magnitude. Y1 - 2012 U6 - https://doi.org/10.1017/S1471068412000142 SN - 1471-0684 VL - 12 SP - 485 EP - 503 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Gebser, Martin A1 - Kaufmann, Benjamin A1 - Schaub, Torsten H. T1 - Multi-threaded ASP solving with clasp JF - Theory and practice of logic programming N2 - We present the new multi-threaded version of the state-of-the-art answer set solver clasp. We detail its component and communication architecture and illustrate how they support the principal functionalities of clasp. Also, we provide some insights into the data representation used for different constraint types handled by clasp. All this is accompanied by an extensive experimental analysis of the major features related to multi-threading in clasp. Y1 - 2012 U6 - https://doi.org/10.1017/S1471068412000166 SN - 1471-0684 VL - 12 IS - 8 SP - 525 EP - 545 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Hoos, Holger A1 - Lindauer, Marius A1 - Schaub, Torsten H. T1 - claspfolio 2 BT - advances in algorithm selection for answer set programming JF - Theory and practice of logic programming N2 - Building on the award-winning, portfolio-based ASP solver claspfolio, we present claspfolio 2, a modular and open solver architecture that integrates several different portfolio-based algorithm selection approaches and techniques. The claspfolio 2 solver framework supports various feature generators, solver selection approaches, solver portfolios, as well as solver-schedule-based pre-solving techniques. The default configuration of claspfolio 2 relies on a light-weight version of the ASP solver clasp to generate static and dynamic instance features. The flexible open design of claspfolio 2 is a distinguishing factor even beyond ASP. As such, it provides a unique framework for comparing and combining existing portfolio-based algorithm selection approaches and techniques in a single, unified framework. Taking advantage of this, we conducted an extensive experimental study to assess the impact of different feature sets, selection approaches and base solver portfolios. In addition to gaining substantial insights into the utility of the various approaches and techniques, we identified a default configuration of claspfolio 2 that achieves substantial performance gains not only over clasp's default configuration and the earlier version of claspfolio, but also over manually tuned configurations of clasp. Y1 - 2014 U6 - https://doi.org/10.1017/S1471068414000210 SN - 1471-0684 SN - 1475-3081 VL - 14 SP - 569 EP - 585 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Videla, Santiago A1 - Guziolowski, Carito A1 - Eduati, Federica A1 - Thiele, Sven A1 - Gebser, Martin A1 - Nicolas, Jacques A1 - Saez-Rodriguez, Julio A1 - Schaub, Torsten H. A1 - Siegel, Anne T1 - Learning Boolean logic models of signaling networks with ASP JF - Theoretical computer science N2 - Boolean networks provide a simple yet powerful qualitative modeling approach in systems biology. However, manual identification of logic rules underlying the system being studied is in most cases out of reach. Therefore, automated inference of Boolean logical networks from experimental data is a fundamental question in this field. This paper addresses the problem consisting of learning from a prior knowledge network describing causal interactions and phosphorylation activities at a pseudo-steady state, Boolean logic models of immediate-early response in signaling transduction networks. The underlying optimization problem has been so far addressed through mathematical programming approaches and the use of dedicated genetic algorithms. In a recent work we have shown severe limitations of stochastic approaches in this domain and proposed to use Answer Set Programming (ASP), considering a simpler problem setting. Herein, we extend our previous work in order to consider more realistic biological conditions including numerical datasets, the presence of feedback-loops in the prior knowledge network and the necessity of multi-objective optimization. In order to cope with such extensions, we propose several discretization schemes and elaborate upon our previous ASP encoding. Towards real-world biological data, we evaluate the performance of our approach over in silico numerical datasets based on a real and large-scale prior knowledge network. The correctness of our encoding and discretization schemes are dealt with in Appendices A-B. (C) 2014 Elsevier B.V. All rights reserved. KW - Answer set programming KW - Signaling transduction networks KW - Boolean logic models KW - Combinatorial multi-objective optimization KW - Systems biology Y1 - 2015 U6 - https://doi.org/10.1016/j.tcs.2014.06.022 SN - 0304-3975 SN - 1879-2294 VL - 599 SP - 79 EP - 101 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Gebser, Martin A1 - Schaub, Torsten H. A1 - Thiele, Sven A1 - Veber, Philippe T1 - Detecting inconsistencies in large biological networks with answer set programming JF - Theory and practice of logic programming N2 - We introduce an approach to detecting inconsistencies in large biological networks by using answer set programming. To this end, we build upon a recently proposed notion of consistency between biochemical/genetic reactions and high-throughput profiles of cell activity. We then present an approach based on answer set programming to check the consistency of large-scale data sets. Moreover, we extend this methodology to provide explanations for inconsistencies by determining minimal representations of conflicts. In practice, this can be used to identify unreliable data or to indicate missing reactions. KW - answer set programming KW - bioinformatics KW - consistency KW - diagnosis Y1 - 2011 U6 - https://doi.org/10.1017/S1471068410000554 SN - 1471-0684 VL - 11 IS - 5-6 SP - 323 EP - 360 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Gebser, Martin A1 - Kaufmann, Benjamin A1 - Kaminski, Roland A1 - Ostrowski, Max A1 - Schaub, Torsten H. A1 - Schneider, Marius T1 - Potassco the Potsdam answer set solving collection JF - AI communications : AICOM ; the European journal on artificial intelligence N2 - This paper gives an overview of the open source project Potassco, the Potsdam Answer Set Solving Collection, bundling tools for Answer Set Programming developed at the University of Potsdam. KW - Answer set programming KW - declarative problem solving Y1 - 2011 U6 - https://doi.org/10.3233/AIC-2011-0491 SN - 0921-7126 VL - 24 IS - 2 SP - 107 EP - 124 PB - IOS Press CY - Amsterdam ER - TY - JOUR A1 - Gebser, Martin A1 - Sabuncu, Orkunt A1 - Schaub, Torsten H. T1 - An incremental answer set programming based system for finite model computation JF - AI communications : AICOM ; the European journal on artificial intelligence N2 - We address the problem of Finite Model Computation (FMC) of first-order theories and show that FMC can efficiently and transparently be solved by taking advantage of a recent extension of Answer Set Programming (ASP), called incremental Answer Set Programming (iASP). The idea is to use the incremental parameter in iASP programs to account for the domain size of a model. The FMC problem is then successively addressed for increasing domain sizes until an answer set, representing a finite model of the original first-order theory, is found. We implemented a system based on the iASP solver iClingo and demonstrate its competitiveness by showing that it slightly outperforms the winner of the FNT division of CADE's 2009 Automated Theorem Proving (ATP) competition on the respective benchmark collection. KW - Incremental answer set programming KW - finite model computation Y1 - 2011 U6 - https://doi.org/10.3233/AIC-2011-0496 SN - 0921-7126 VL - 24 IS - 2 SP - 195 EP - 212 PB - IOS Press CY - Amsterdam ER - TY - JOUR A1 - Lindauer, Marius A1 - Hoos, Holger H. A1 - Hutter, Frank A1 - Schaub, Torsten H. T1 - An automatically configured algorithm selector JF - The journal of artificial intelligence research N2 - Algorithm selection (AS) techniques - which involve choosing from a set of algorithms the one expected to solve a given problem instance most efficiently - have substantially improved the state of the art in solving many prominent AI problems, such as SAT, CSP, ASP, MAXSAT and QBF. Although several AS procedures have been introduced, not too surprisingly, none of them dominates all others across all AS scenarios. Furthermore, these procedures have parameters whose optimal values vary across AS scenarios. This holds specifically for the machine learning techniques that form the core of current AS procedures, and for their hyperparameters. Therefore, to successfully apply AS to new problems, algorithms and benchmark sets, two questions need to be answered: (i) how to select an AS approach and (ii) how to set its parameters effectively. We address both of these problems simultaneously by using automated algorithm configuration. Specifically, we demonstrate that we can automatically configure claspfolio 2, which implements a large variety of different AS approaches and their respective parameters in a single, highly-parameterized algorithm framework. Our approach, dubbed AutoFolio, allows researchers and practitioners across a broad range of applications to exploit the combined power of many different AS methods. We demonstrate AutoFolio can significantly improve the performance of claspfolio 2 on 8 out of the 13 scenarios from the Algorithm Selection Library, leads to new state-of-the-art algorithm selectors for 7 of these scenarios, and matches state-of-the-art performance (statistically) on all other scenarios. Compared to the best single algorithm for each AS scenario, AutoFolio achieves average speedup factors between 1.3 and 15.4. Y1 - 2015 SN - 1076-9757 SN - 1943-5037 VL - 53 SP - 745 EP - 778 PB - AI Access Foundation CY - Marina del Rey ER - TY - JOUR A1 - Hoos, Holger A1 - Kaminski, Roland A1 - Lindauer, Marius A1 - Schaub, Torsten H. T1 - aspeed: Solver scheduling via answer set programming JF - Theory and practice of logic programming N2 - Although Boolean Constraint Technology has made tremendous progress over the last decade, the efficacy of state-of-the-art solvers is known to vary considerably across different types of problem instances, and is known to depend strongly on algorithm parameters. This problem was addressed by means of a simple, yet effective approach using handmade, uniform, and unordered schedules of multiple solvers in ppfolio, which showed very impressive performance in the 2011 Satisfiability Testing (SAT) Competition. Inspired by this, we take advantage of the modeling and solving capacities of Answer Set Programming (ASP) to automatically determine more refined, that is, nonuniform and ordered solver schedules from the existing benchmarking data. We begin by formulating the determination of such schedules as multi-criteria optimization problems and provide corresponding ASP encodings. The resulting encodings are easily customizable for different settings, and the computation of optimum schedules can mostly be done in the blink of an eye, even when dealing with large runtime data sets stemming from many solvers on hundreds to thousands of instances. Also, the fact that our approach can be customized easily enabled us to swiftly adapt it to generate parallel schedules for multi-processor machines. KW - algorithm schedules KW - answer set programming KW - portfolio-based solving Y1 - 2015 U6 - https://doi.org/10.1017/S1471068414000015 SN - 1471-0684 SN - 1475-3081 VL - 15 SP - 117 EP - 142 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Schaub, Torsten H. A1 - Wang, Kewen T1 - A comparative study of logic programs with preference Y1 - 2001 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. T1 - How to reason credulously and skeptically within a single extension. Y1 - 2001 SN - 3-540- 42464-4 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. A1 - Tompits, Hans T1 - A generic compiler for ordered logic programs Y1 - 2001 SN - 3-540-42593-4 ER - TY - JOUR A1 - Schaub, Torsten H. A1 - Wang, Kewen T1 - A comparative study of logic programs with preference Y1 - 2001 SN - 1-558-60777-3 SN - 1045-0823 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. T1 - How to reason credulously and skeptically within a single extension Y1 - 2001 ER - TY - JOUR A1 - Besnard, Philippe A1 - Schaub, Torsten H. T1 - Significant inferences Y1 - 2000 SN - 1-55860-690-4 ER - TY - JOUR A1 - Linke, Thomas A1 - Schaub, Torsten H. T1 - Alternative foundations for Reiter's default logic. Y1 - 2000 SN - 0004-3702 ER - TY - JOUR A1 - Besnard, Philippe A1 - Schaub, Torsten H. T1 - What is a (non-constructive) non-monotone logical system? Y1 - 2000 SN - 0304-3975 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. T1 - The role of default logic in knowledge representation Y1 - 2000 SN - 0-7923-7224-7 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. T1 - Expressing preferences in default logic Y1 - 2000 SN - 0004-3702 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. A1 - Tompits, Hans T1 - A compilation of Brewka and Eiter's approach to prioritizationtion Y1 - 2000 SN - 3-540-41131-3 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. T1 - A consistency-based model for belief change: preliminary report Y1 - 2000 SN - 0-262-51112-6 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. A1 - Tompits, Hans T1 - Logic programs with compiled preferences Y1 - 2000 SN - 1-58603-013-2 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. A1 - Tompits, Hans T1 - Logic programs with compiled preferences Y1 - 2000 UR - http://xxx.lanl.gov/abs/cs.AI/0003028 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. T1 - A consistency-based model for belief change: preliminary report Y1 - 2000 UR - http://xxx.lanl.gov/abs/cs.AI/0003052 ER - TY - JOUR A1 - Delgrande, James Patrick A1 - Schaub, Torsten H. A1 - Tompits, Hans T1 - A compiler for ordered logic programs Y1 - 2000 UR - http://arxiv.org/abs/cs.AI/0003024 ER - TY - JOUR A1 - Brüning, Stefan A1 - Schaub, Torsten H. T1 - A connection calculus for handling incomplete information Y1 - 2000 ER - TY - JOUR A1 - Brüning, Stefan A1 - Schaub, Torsten H. T1 - Avoiding non-ground variables Y1 - 1999 SN - 3-540-66131-x ER - TY - JOUR A1 - Benhammadi, Farid A1 - Nicolas, Pascal A1 - Schaub, Torsten H. T1 - Query-answering in prioritized default logic Y1 - 1999 SN - 3-540-66131-X ER - TY - BOOK A1 - Schaub, Torsten H. T1 - The automation of reasoning with incomplete information : from semantic foundations to efficient computation T3 - Lecture notes in computer science Y1 - 1999 SN - 3-540-64515-2 U6 - https://doi.org/10.1007/BFb0054963 VL - 1409 PB - Springer CY - Berlin ER - TY - JOUR A1 - Benhammadi, Farid A1 - Nicolas, Pascal A1 - Schaub, Torsten H. T1 - Query-answering in prioritized default logic Y1 - 1999 SN - 3-540-66131-X ER - TY - JOUR A1 - Brüning, Stefan A1 - Schaub, Torsten H. T1 - A voiding non-ground variables Y1 - 1999 ER - TY - JOUR A1 - Linke, Thomas A1 - Schaub, Torsten H. T1 - On bottom-up pre-processing techniques for automated default reasoning Y1 - 1999 SN - 3-540-66131-x ER - TY - JOUR A1 - Brewka, Gerhard A1 - Ellmauthaler, Stefan A1 - Kern-Isberner, Gabriele A1 - Obermeier, Philipp A1 - Ostrowski, Max A1 - Romero, Javier A1 - Schaub, Torsten H. A1 - Schieweck, Steffen T1 - Advanced solving technology for dynamic and reactive applications JF - Künstliche Intelligenz Y1 - 2018 U6 - https://doi.org/10.1007/s13218-018-0538-8 SN - 0933-1875 SN - 1610-1987 VL - 32 IS - 2-3 SP - 199 EP - 200 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Banbara, Mutsunori A1 - Soh, Takehide A1 - Tamura, Naoyuki A1 - Inoue, Katsumi A1 - Schaub, Torsten H. T1 - Answer set programming as a modeling language for course timetabling JF - Theory and practice of logic programming N2 - The course timetabling problem can be generally defined as the task of assigning a number of lectures to a limited set of timeslots and rooms, subject to a given set of hard and soft constraints. The modeling language for course timetabling is required to be expressive enough to specify a wide variety of soft constraints and objective functions. Furthermore, the resulting encoding is required to be extensible for capturing new constraints and for switching them between hard and soft, and to be flexible enough to deal with different formulations. In this paper, we propose to make effective use of ASP as a modeling language for course timetabling. We show that our ASP-based approach can naturally satisfy the above requirements, through an ASP encoding of the curriculum-based course timetabling problem proposed in the third track of the second international timetabling competition (ITC-2007). Our encoding is compact and human-readable, since each constraint is individually expressed by either one or two rules. Each hard constraint is expressed by using integrity constraints and aggregates of ASP. Each soft constraint S is expressed by rules in which the head is the form of penalty (S, V, C), and a violation V and its penalty cost C are detected and calculated respectively in the body. We carried out experiments on four different benchmark sets with five different formulations. We succeeded either in improving the bounds or producing the same bounds for many combinations of problem instances and formulations, compared with the previous best known bounds. KW - answer set programming KW - educational timetabling KW - course timetabling Y1 - 2013 U6 - https://doi.org/10.1017/S1471068413000495 SN - 1471-0684 VL - 13 IS - 2 SP - 783 EP - 798 PB - Cambridge Univ. Press CY - New York ER - TY - GEN A1 - Bosser, Anne-Gwenn A1 - Cabalar, Pedro A1 - Dieguez, Martin A1 - Schaub, Torsten H. T1 - Introducing temporal stable models for linear dynamic logic T2 - 16th International Conference on Principles of Knowledge Representation and Reasoning N2 - We propose a new temporal extension of the logic of Here-and-There (HT) and its equilibria obtained by combining it with dynamic logic over (linear) traces. Unlike previous temporal extensions of HT based on linear temporal logic, the dynamic logic features allow us to reason about the composition of actions. For instance, this can be used to exercise fine grained control when planning in robotics, as exemplified by GOLOG. In this paper, we lay the foundations of our approach, and refer to it as Linear Dynamic Equilibrium Logic, or simply DEL. We start by developing the formal framework of DEL and provide relevant characteristic results. Among them, we elaborate upon the relationships to traditional linear dynamic logic and previous temporal extensions of HT. Y1 - 2018 UR - https://www.dc.fi.udc.es/~cabalar/del.pdf SP - 12 EP - 21 PB - ASSOC Association for the Advancement of Artificial Intelligence CY - Palo Alto ER - TY - JOUR A1 - Fandiño, Jorge A1 - Lifschitz, Vladimir A1 - Lühne, Patrick A1 - Schaub, Torsten H. T1 - Verifying tight logic programs with Anthem and Vampire JF - Theory and practice of logic programming N2 - This paper continues the line of research aimed at investigating the relationship between logic programs and first-order theories. We extend the definition of program completion to programs with input and output in a subset of the input language of the ASP grounder gringo, study the relationship between stable models and completion in this context, and describe preliminary experiments with the use of two software tools, anthem and vampire, for verifying the correctness of programs with input and output. Proofs of theorems are based on a lemma that relates the semantics of programs studied in this paper to stable models of first-order formulas. Y1 - 2020 U6 - https://doi.org/10.1017/S1471068420000344 SN - 1471-0684 SN - 1475-3081 VL - 20 IS - 5 SP - 735 EP - 750 PB - Cambridge Univ. Press CY - Cambridge [u.a.] ER - TY - JOUR A1 - Cabalar, Pedro A1 - Fandiño, Jorge A1 - Garea, Javier A1 - Romero, Javier A1 - Schaub, Torsten H. T1 - Eclingo BT - a solver for epistemic logic programs JF - Theory and practice of logic programming N2 - We describe eclingo, a solver for epistemic logic programs under Gelfond 1991 semantics built upon the Answer Set Programming system clingo. The input language of eclingo uses the syntax extension capabilities of clingo to define subjective literals that, as usual in epistemic logic programs, allow for checking the truth of a regular literal in all or in some of the answer sets of a program. The eclingo solving process follows a guess and check strategy. It first generates potential truth values for subjective literals and, in a second step, it checks the obtained result with respect to the cautious and brave consequences of the program. This process is implemented using the multi-shot functionalities of clingo. We have also implemented some optimisations, aiming at reducing the search space and, therefore, increasing eclingo 's efficiency in some scenarios. Finally, we compare the efficiency of eclingo with two state-of-the-art solvers for epistemic logic programs on a pair of benchmark scenarios and show that eclingo generally outperforms their obtained results. KW - Answer Set Programming KW - Epistemic Logic Programs KW - Non-Monotonic KW - Reasoning KW - Conformant Planning Y1 - 2020 U6 - https://doi.org/10.1017/S1471068420000228 SN - 1471-0684 SN - 1475-3081 VL - 20 IS - 6 SP - 834 EP - 847 PB - Cambridge Univ. Press CY - New York ER - TY - JOUR A1 - Cabalar, Pedro A1 - Fandiño, Jorge A1 - Schaub, Torsten H. A1 - Schellhorn, Sebastian T1 - Gelfond-Zhang aggregates as propositional formulas JF - Artificial intelligence N2 - Answer Set Programming (ASP) has become a popular and widespread paradigm for practical Knowledge Representation thanks to its expressiveness and the available enhancements of its input language. One of such enhancements is the use of aggregates, for which different semantic proposals have been made. In this paper, we show that any ASP aggregate interpreted under Gelfond and Zhang's (GZ) semantics can be replaced (under strong equivalence) by a propositional formula. Restricted to the original GZ syntax, the resulting formula is reducible to a disjunction of conjunctions of literals but the formulation is still applicable even when the syntax is extended to allow for arbitrary formulas (including nested aggregates) in the condition. Once GZ-aggregates are represented as formulas, we establish a formal comparison (in terms of the logic of Here-and-There) to Ferraris' (F) aggregates, which are defined by a different formula translation involving nested implications. In particular, we prove that if we replace an F-aggregate by a GZ-aggregate in a rule head, we do not lose answer sets (although more can be gained). This extends the previously known result that the opposite happens in rule bodies, i.e., replacing a GZ-aggregate by an F-aggregate in the body may yield more answer sets. Finally, we characterize a class of aggregates for which GZ- and F-semantics coincide. KW - Aggregates KW - Answer Set Programming Y1 - 2019 U6 - https://doi.org/10.1016/j.artint.2018.10.007 SN - 0004-3702 SN - 1872-7921 VL - 274 SP - 26 EP - 43 PB - Elsevier CY - Amsterdam ER - TY - GEN A1 - Cabalar, Pedro A1 - Fandiño, Jorge A1 - Schaub, Torsten H. A1 - Schellhorn, Sebastian T1 - Lower Bound Founded Logic of Here-and-There T2 - Logics in Artificial Intelligence N2 - A distinguishing feature of Answer Set Programming is that all atoms belonging to a stable model must be founded. That is, an atom must not only be true but provably true. This can be made precise by means of the constructive logic of Here-and-There, whose equilibrium models correspond to stable models. One way of looking at foundedness is to regard Boolean truth values as ordered by letting true be greater than false. Then, each Boolean variable takes the smallest truth value that can be proven for it. This idea was generalized by Aziz to ordered domains and applied to constraint satisfaction problems. As before, the idea is that a, say integer, variable gets only assigned to the smallest integer that can be justified. In this paper, we present a logical reconstruction of Aziz’ idea in the setting of the logic of Here-and-There. More precisely, we start by defining the logic of Here-and-There with lower bound founded variables along with its equilibrium models and elaborate upon its formal properties. Finally, we compare our approach with related ones and sketch future work. Y1 - 2019 SN - 978-3-030-19570-0 SN - 978-3-030-19569-4 U6 - https://doi.org/10.1007/978-3-030-19570-0_34 SN - 0302-9743 SN - 1611-3349 VL - 11468 SP - 509 EP - 525 PB - Springer CY - Cham ER -