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Documents authored by Janhunen, Tomi

Document
DOI: 10.4230/LIPIcs.TIME.2019.14
On the Utility of Neighbourhood Singleton-Style Consistencies for Qualitative Constraint-Based Spatial and Temporal Reasoning

Authors: Michael Sioutis, Anastasia Paparrizou, and Tomi Janhunen

Published in: LIPIcs, Volume 147, 26th International Symposium on Temporal Representation and Reasoning (TIME 2019)

Abstract
A singleton-style consistency is a local consistency that verifies if each base relation (atom) of each constraint of a qualitative constraint network (QCN) can serve as a support with respect to the closure of that network under a (naturally) weaker local consistency. This local consistency is essential for tackling fundamental reasoning problems associated with QCNs, such as the satisfiability checking or the minimal labeling problem, but can suffer from redundant constraint checks, especially when those checks occur far from where the pruning usually takes place. In this paper, we propose singleton-style consistencies that are applied just on the neighbourhood of a singleton-checked constraint instead of the whole network. We make a theoretical comparison with existing consistencies and consequently prove some properties of the new ones. In addition, we propose algorithms to enforce our consistencies, as well as parsimonious variants thereof, that are more efficient in practice than the state of the art. We make an experimental evaluation with random and structured QCNs of Interval Algebra in the phase transition region to demonstrate the potential of our approach.
Cite as

Michael Sioutis, Anastasia Paparrizou, and Tomi Janhunen. On the Utility of Neighbourhood Singleton-Style Consistencies for Qualitative Constraint-Based Spatial and Temporal Reasoning. In 26th International Symposium on Temporal Representation and Reasoning (TIME 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 147, pp. 14:1-14:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{sioutis_et_al:LIPIcs.TIME.2019.14,
  author =	{Sioutis, Michael and Paparrizou, Anastasia and Janhunen, Tomi},
  title =	{{On the Utility of Neighbourhood Singleton-Style Consistencies for Qualitative Constraint-Based Spatial and Temporal Reasoning}},
  booktitle =	{26th International Symposium on Temporal Representation and Reasoning (TIME 2019)},
  pages =	{14:1--14:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-127-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{147},
  editor =	{Gamper, Johann and Pinchinat, Sophie and Sciavicco, Guido},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2019.14},
  URN =		{urn:nbn:de:0030-drops-113727},
  doi =		{10.4230/LIPIcs.TIME.2019.14},
  annote =	{Keywords: Qualitative constraints, spatial and temporal reasoning, singleton-style consistencies, neighbourhood, minimal labeling problem}
}
Document
DOI: 10.4230/OASIcs.ICLP.2016.5
Rewriting Optimization Statements in Answer-Set Programs

Authors: Jori Bomanson, Martin Gebser, and Tomi Janhunen

Published in: OASIcs, Volume 52, Technical Communications of the 32nd International Conference on Logic Programming (ICLP 2016)

Abstract
Constraints on Pseudo-Boolean (PB) expressions can be translated into Conjunctive Normal Form (CNF) using several known translations. In Answer-Set Programming (ASP), analogous expressions appear in weight rules and optimization statements. Previously, we have translated weight rules into normal rules, using normalizations designed in accord with existing CNF encodings. In this work, we rededicate such designs to rewrite optimization statements in ASP. In this context, a rewrite of an optimization statement is a replacement accompanied by a set of normal rules that together replicate the original meaning. The goal is partially the same as in translating PB constraints or weight rules: to introduce new meaningful auxiliary atoms that may help a solver in the search for (optimal) solutions. In addition to adapting previous translations, we present selective rewriting techniques in order to meet the above goal while using only a limited amount of new rules and atoms. We experimentally evaluate these methods in preprocessing ASP optimization statements and then searching for optimal answer sets. The results exhibit significant advances in terms of numbers of optimally solved instances, reductions in search conflicts, and shortened computation times. By appropriate choices of rewriting techniques, improvements are made on instances involving both small and large weights. In particular, we show that selective rewriting is paramount on benchmarks involving large weights.
Cite as

Jori Bomanson, Martin Gebser, and Tomi Janhunen. Rewriting Optimization Statements in Answer-Set Programs. In Technical Communications of the 32nd International Conference on Logic Programming (ICLP 2016). Open Access Series in Informatics (OASIcs), Volume 52, pp. 5:1-5:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{bomanson_et_al:OASIcs.ICLP.2016.5,
  author =	{Bomanson, Jori and Gebser, Martin and Janhunen, Tomi},
  title =	{{Rewriting Optimization Statements in Answer-Set Programs}},
  booktitle =	{Technical Communications of the 32nd International Conference on Logic Programming (ICLP 2016)},
  pages =	{5:1--5:15},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-007-1},
  ISSN =	{2190-6807},
  year =	{2016},
  volume =	{52},
  editor =	{Carro, Manuel and King, Andy and Saeedloei, Neda and De Vos, Marina},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.ICLP.2016.5},
  URN =		{urn:nbn:de:0030-drops-67362},
  doi =		{10.4230/OASIcs.ICLP.2016.5},
  annote =	{Keywords: Answer-Set Programming, Pseudo-Boolean optimization, Translation methods}
}
Document
DOI: 10.4230/LIPIcs.ICLP.2010.94
Sampler Programs: The Stable Model Semantics of Abstract Constraint Programs Revisited

Authors: Tomi Janhunen

Published in: LIPIcs, Volume 7, Technical Communications of the 26th International Conference on Logic Programming (2010)

Abstract
Abstract constraint atoms provide a general framework for the study of aggregates utilized in answer set programming. Such primitives suitably increase the expressive power of rules and enable more concise representation of various domains as answer set programs. However, it is non-trivial to generalize the stable model semantics for programs involving arbitrary abstract constraint atoms. For instance, a nondeterministic variant of the immediate consequence operator is needed, or the definition of stable models cannot be stated directly using primitives of logic programs. In this paper, we propose sampler programs as a relaxation of abstract constraint programs that better lend themselves to the program transformation involved in the definition of stable models. Consequently, the declarative nature of stable models can be restored for sampler programs and abstract constraint programs are also covered if decomposed into sampler programs. Moreover, we study the relationships of the classes of programs involved and provide a characterization in terms of abstract but essentially deterministic computations. This result indicates that all nondeterminism related with abstract constraint atoms can be resolved at the level of program reduct when sampler programs are used as the intermediate representation.
Cite as

Tomi Janhunen. Sampler Programs: The Stable Model Semantics of Abstract Constraint Programs Revisited. In Technical Communications of the 26th International Conference on Logic Programming. Leibniz International Proceedings in Informatics (LIPIcs), Volume 7, pp. 94-103, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2010)

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@InProceedings{janhunen:LIPIcs.ICLP.2010.94,
  author =	{Janhunen, Tomi},
  title =	{{Sampler Programs: The Stable Model Semantics of Abstract Constraint Programs Revisited}},
  booktitle =	{Technical Communications of the 26th International Conference on Logic Programming},
  pages =	{94--103},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-17-0},
  ISSN =	{1868-8969},
  year =	{2010},
  volume =	{7},
  editor =	{Hermenegildo, Manuel and Schaub, Torsten},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICLP.2010.94},
  URN =		{urn:nbn:de:0030-drops-25871},
  doi =		{10.4230/LIPIcs.ICLP.2010.94},
  annote =	{Keywords: Stable models, abstract constraints, program reduction, translation, choice rules}
}
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