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Documents authored by Sioutis, Michael


Document
Prime Scenarios in Qualitative Spatial and Temporal Reasoning

Authors: Yakoub Salhi and Michael Sioutis

Published in: LIPIcs, Volume 278, 30th International Symposium on Temporal Representation and Reasoning (TIME 2023)


Abstract
The concept of prime implicant is a fundamental tool in Boolean algebra, which is used in Boolean circuit design and, recently, in explainable AI. This study investigates an analogous concept in qualitative spatial and temporal reasoning, called prime scenario. Specifically, we define a prime scenario of a qualitative constraint network (QCN) as a minimal set of decisions that can uniquely determine solutions of this QCN. We propose in this paper a collection of algorithms designed to address various problems related to prime scenarios. The first three algorithms aim to generate a prime scenario from a scenario of a QCN. The main idea consists in using path consistency to identify the constraints that can be ignored to generate a prime scenario. The next two algorithms focus on generating a set of prime scenarios that cover all the scenarios of the original QCN: The first algorithm examines every branch of the search tree, while the second is based on the use of a SAT encoding. Our last algorithm is concerned with computing a minimum-size prime scenario by using a MaxSAT encoding built from countermodels of the original QCN. We show that this algorithm is particularly useful for measuring the robustness of a QCN. Finally, a preliminary experimental evaluation is performed with instances of Allen’s Interval Algebra to assess the efficiency of our algorithms and, hence, also the difficulty of the newly introduced problems here.

Cite as

Yakoub Salhi and Michael Sioutis. Prime Scenarios in Qualitative Spatial and Temporal Reasoning. In 30th International Symposium on Temporal Representation and Reasoning (TIME 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 278, pp. 5:1-5:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


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@InProceedings{salhi_et_al:LIPIcs.TIME.2023.5,
  author =	{Salhi, Yakoub and Sioutis, Michael},
  title =	{{Prime Scenarios in Qualitative Spatial and Temporal Reasoning}},
  booktitle =	{30th International Symposium on Temporal Representation and Reasoning (TIME 2023)},
  pages =	{5:1--5:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-298-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{278},
  editor =	{Artikis, Alexander and Bruse, Florian and Hunsberger, Luke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2023.5},
  URN =		{urn:nbn:de:0030-drops-190957},
  doi =		{10.4230/LIPIcs.TIME.2023.5},
  annote =	{Keywords: Spatial and Temporal Reasoning, Qualitative Constraints, Prime Scenario, Prime Implicant, Robustness Measurement}
}
Document
Embarrassingly Greedy Inconsistency Resolution of Qualitative Constraint Networks

Authors: Michael Sioutis

Published in: LIPIcs, Volume 278, 30th International Symposium on Temporal Representation and Reasoning (TIME 2023)


Abstract
In this paper, we deal with inconsistency resolution in qualitative constraint networks (QCN). This type of networks allows one to represent and reason about spatial or temporal information in a natural, human-like manner, e.g., by expressing relations of the form x {is north of ∨ is east of} y. On the other hand, inconsistency resolution involves maximizing the amount of information that is consistent in a knowledge base; in the context of QCNs, this translates to maximizing the number of constraints that can be satisfied, via obtaining a qualitative solution (scenario) of the QCN that ignores/violates as few of the original constraints as possible. To this end, we present two novel approaches: a greedy constraint-based and an optimal Partial MaxSAT-based one, with a focus on the former due to its simplicity. Specifically, the greedy technique consists in adding the constraints of a QCN to a new, initially empty network, one by one, all the while filtering out the ones that fail the satisfiability check. What makes or breaks this technique is the ordering in which the constraints will be processed to saturate the empty QCN, and for that purpose we use many different strategies to form a portfolio-style implementation. The Partial MaxSAT-based approach is powered by Horn theory-based maximal tractable subsets of relations. Finally, we compare the greedy approach with the optimal one, commenting on the trade-off between obtaining repairs that are optimal and obtaining repairs in a manner that is fast, and make our source code available for anyone to use.

Cite as

Michael Sioutis. Embarrassingly Greedy Inconsistency Resolution of Qualitative Constraint Networks. In 30th International Symposium on Temporal Representation and Reasoning (TIME 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 278, pp. 12:1-12:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


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@InProceedings{sioutis:LIPIcs.TIME.2023.12,
  author =	{Sioutis, Michael},
  title =	{{Embarrassingly Greedy Inconsistency Resolution of Qualitative Constraint Networks}},
  booktitle =	{30th International Symposium on Temporal Representation and Reasoning (TIME 2023)},
  pages =	{12:1--12:12},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-298-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{278},
  editor =	{Artikis, Alexander and Bruse, Florian and Hunsberger, Luke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2023.12},
  URN =		{urn:nbn:de:0030-drops-191020},
  doi =		{10.4230/LIPIcs.TIME.2023.12},
  annote =	{Keywords: Spatial and Temporal Reasoning, Qualitative Constraints, Inconsistency Resolution, Maximizing Satisfiability, Greedy Algorithm, Partial MaxSAT Solver}
}
Document
Extended Abstract
A Decomposition Framework for Inconsistency Handling in Qualitative Spatial and Temporal Reasoning (Extended Abstract)

Authors: Yakoub Salhi and Michael Sioutis

Published in: LIPIcs, Volume 278, 30th International Symposium on Temporal Representation and Reasoning (TIME 2023)


Abstract
Dealing with inconsistency is a central problem in AI, due to the fact that inconsistency can arise for many reasons in real-world applications, such as context dependency, multi-source information, vagueness, noisy data, etc. Among the approaches that are involved in inconsistency handling, we can mention argumentation, non-monotonic reasoning, and paraconsistency, e.g., see [Philippe Besnard and Anthony Hunter, 2008; Gerhard Brewka et al., 1997; Koji Tanaka et al., 2013]. In the work of [Yakoub Salhi and Michael Sioutis, 2023], we are interested in dealing with inconsistency in the context of Qualitative Spatio-Temporal Reasoning (QSTR) [Ligozat, 2013]. QSTR is an AI framework that aims to mimic, natural, human-like representation and reasoning regarding space and time. This framework is applied to a variety of domains, such as qualitative case-based reasoning and learning [Thiago Pedro Donadon Homem et al., 2020] and visual sensemaking [Jakob Suchan et al., 2021]; the interested reader is referred to [Michael Sioutis and Diedrich Wolter, 2021] for a recent survey. Motivation. In [Yakoub Salhi and Michael Sioutis, 2023], we study the decomposition of an inconsistent constraint network into consistent subnetworks under, possible, mandatory constraints. To illustrate the interest of such a decomposition, we provide a simple example described in Figure 1. The QCN depicted in the top part of the figure corresponds to a description of an inconsistent plan. Further, we assume that the constraint Task A {before} Task B is mandatory. To handle inconsistency, this plan can be transformed into a decomposition of two consistent plans, depicted in the bottom part of the figure; this decomposition can be used, e.g., to capture the fact that Task C must be performed twice. More generally, network decomposition can be involved in inconsistency handling in several ways: it can be used to identify potential contexts that explain the presence of inconsistent information; it can also be used to restore consistency through a compromise between the components of a decomposition, e.g., by using belief merging [Jean-François Condotta et al., 2010]; in addition, QCN decomposition can be used as the basis for defining inconsistency measures. Contributions. We summarize the contributions of [Yakoub Salhi and Michael Sioutis, 2023] as follows. First, we propose a theoretical study of a problem that consists in decomposing an inconsistent QCN into a bounded number of consistent QCNs that may satisfy a specified part in the original QCN; intuitively, the required common part corresponds to the constraints that are considered necessary, if any. To this end, we provide upper bounds for the minimum number of components in a decomposition as well as computational complexity results. Secondly, we provide two methods for solving our decomposition problem. The first method corresponds to a greedy constraint-based algorithm, a variant of which involves the use of spanning trees; the basic idea of this variant is that any acyclic constraint graph in QSTR is consistent, and such a graph can be used as a starting point for building consistent components. The second method corresponds to a SAT-based encoding; every model of this encoding is used to construct a valid decomposition. Thirdly, we consider two optimization versions of the initial decomposition problem that focus on minimizing the number of components and maximizing the similarity between components, respectively. The similarity between two QCNs is quantified by the number of common non-universal constraints; the interest in maximizing the similarity lies mainly in the fact that it reduces the number of constraints that allow each component to be distinguished from the rest. Of course, our previous methods are adapted to tackle these optimization versions, too. Additionally, we introduce two inconsistency measures based on QCN decomposition, which can be seen as counterparts of measures for propositional KBs introduced in [Matthias Thimm, 2016; Meriem Ammoura et al., 2017], and show that they satisfy several desired properties in the literature. Finally, we provide implementations of our methods for computing decompositions and experimentally evaluate them using different metrics.

Cite as

Yakoub Salhi and Michael Sioutis. A Decomposition Framework for Inconsistency Handling in Qualitative Spatial and Temporal Reasoning (Extended Abstract). In 30th International Symposium on Temporal Representation and Reasoning (TIME 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 278, pp. 16:1-16:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)


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@InProceedings{salhi_et_al:LIPIcs.TIME.2023.16,
  author =	{Salhi, Yakoub and Sioutis, Michael},
  title =	{{A Decomposition Framework for Inconsistency Handling in Qualitative Spatial and Temporal Reasoning}},
  booktitle =	{30th International Symposium on Temporal Representation and Reasoning (TIME 2023)},
  pages =	{16:1--16:3},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-298-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{278},
  editor =	{Artikis, Alexander and Bruse, Florian and Hunsberger, Luke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2023.16},
  URN =		{urn:nbn:de:0030-drops-191062},
  doi =		{10.4230/LIPIcs.TIME.2023.16},
  annote =	{Keywords: Spatial and Temporal Reasoning, Qualitative Constraints, Inconsistency Handling, Decomposition, Inconsistency Measures}
}
Document
An Incremental Algorithm for Handling Qualitative Spatio-Temporal Information

Authors: Zhiguo Long, Qiyuan Hu, Hua Meng, and Michael Sioutis

Published in: LIPIcs, Volume 240, 15th International Conference on Spatial Information Theory (COSIT 2022)


Abstract
In this paper, we present an online (incremental) algorithm for checking the satisfiability of qualitative spatio-temporal data, with direct implications to other fundamental knowledge representation and reasoning problems for such data, like the problems of deductive closure and redundancy removal. In particular, qualitative data come in the form of human-like, symbolic, descriptions such as "region x contains or overlaps region y", which are abundant in the Web of Data. Our approach is also able to maintain, to some extent, any sparse graph structure that may be inherent in the data, i.e., it acts parsimoniously and only tries to infer new information when needed for soundness and completeness. To this end, we complement our practical algorithm with certain theoretical results to assert its correctness and efficiency. A subsequent evaluation with publicly available large-scale real-world and random datasets against the state of the art, shows the interest and promise of our method.

Cite as

Zhiguo Long, Qiyuan Hu, Hua Meng, and Michael Sioutis. An Incremental Algorithm for Handling Qualitative Spatio-Temporal Information. In 15th International Conference on Spatial Information Theory (COSIT 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 240, pp. 5:1-5:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)


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@InProceedings{long_et_al:LIPIcs.COSIT.2022.5,
  author =	{Long, Zhiguo and Hu, Qiyuan and Meng, Hua and Sioutis, Michael},
  title =	{{An Incremental Algorithm for Handling Qualitative Spatio-Temporal Information}},
  booktitle =	{15th International Conference on Spatial Information Theory (COSIT 2022)},
  pages =	{5:1--5:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-257-0},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{240},
  editor =	{Ishikawa, Toru and Fabrikant, Sara Irina and Winter, Stephan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.COSIT.2022.5},
  URN =		{urn:nbn:de:0030-drops-168907},
  doi =		{10.4230/LIPIcs.COSIT.2022.5},
  annote =	{Keywords: Online algorithm, qualitative data, spatio-temporal reasoning, satisfiability checking, knowledge representation and reasoning}
}
Document
Dynamic Branching in Qualitative Constraint Networks via Counting Local Models

Authors: Michael Sioutis and Diedrich Wolter

Published in: LIPIcs, Volume 178, 27th International Symposium on Temporal Representation and Reasoning (TIME 2020)


Abstract
We introduce and evaluate dynamic branching strategies for solving Qualitative Constraint Networks (QCNs), which are networks that are mostly used to represent and reason about spatial and temporal information via the use of simple qualitative relations, e.g., a constraint can be "Task A is scheduled after or during Task C". In qualitative constraint-based reasoning, the state-of-the-art approach to tackle a given QCN consists in employing a backtracking algorithm, where the branching decisions during search are governed by the restrictiveness of the possible relations for a given constraint (e.g., after can be more restrictive than during). In the literature, that restrictiveness is defined a priori by means of static weights that are precomputed and associated with the relations of a given calculus, without any regard to the particulars of a given network instance of that calculus, such as its structure. In this paper, we address this limitation by proposing heuristics that dynamically associate a weight with a relation, based on the count of local models (or local scenarios) that the relation is involved with in a given QCN; these models are local in that they focus on triples of variables instead of the entire QCN. Therefore, our approach is adaptive and seeks to make branching decisions that preserve most of the solutions by determining what proportion of local solutions agree with that decision. Experimental results with a random and a structured dataset of QCNs of Interval Algebra show that it is possible to achieve up to 5 times better performance for structured instances, whilst maintaining non-negligible gains of around 20% for random ones.

Cite as

Michael Sioutis and Diedrich Wolter. Dynamic Branching in Qualitative Constraint Networks via Counting Local Models. In 27th International Symposium on Temporal Representation and Reasoning (TIME 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 178, pp. 12:1-12:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)


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@InProceedings{sioutis_et_al:LIPIcs.TIME.2020.12,
  author =	{Sioutis, Michael and Wolter, Diedrich},
  title =	{{Dynamic Branching in Qualitative Constraint Networks via Counting Local Models}},
  booktitle =	{27th International Symposium on Temporal Representation and Reasoning (TIME 2020)},
  pages =	{12:1--12:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-167-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{178},
  editor =	{Mu\~{n}oz-Velasco, Emilio and Ozaki, Ana and Theobald, Martin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2020.12},
  URN =		{urn:nbn:de:0030-drops-129802},
  doi =		{10.4230/LIPIcs.TIME.2020.12},
  annote =	{Keywords: Qualitative constraints, spatial and temporal reasoning, counting local models, dynamic branching, adaptive algorithm}
}
Document
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
Collective Singleton-Based Consistency for Qualitative Constraint Networks

Authors: Michael Sioutis, Anastasia Paparrizou, and Jean-François Condotta

Published in: LIPIcs, Volume 90, 24th International Symposium on Temporal Representation and Reasoning (TIME 2017)


Abstract
Partial singleton closure under weak composition, or partial singleton (weak) path-consistency for short, is essential for approximating satisfiability of qualitative constraints networks. Briefly put, partial singleton path-consistency ensures that each base relation of each of the constraints of a qualitative constraint network can define a singleton relation in the corresponding partial closure of that network under weak composition, or in its corresponding partially (weak) path-consistent subnetwork for short. In particular, partial singleton path-consistency has been shown to play a crucial role in tackling the minimal labeling problem of a qualitative constraint network, which is the problem of finding the strongest implied constraints of that network. In this paper, we propose a stronger local consistency that couples partial singleton path-consistency with the idea of collectively deleting certain unfeasible base relations by exploiting singleton checks. We then propose an efficient algorithm for enforcing this consistency that, given a qualitative constraint network, performs fewer constraint checks than the respective algorithm for enforcing partial singleton path-consistency in that network. We formally prove certain properties of our new local consistency, and motivate its usefulness through demonstrative examples and a preliminary experimental evaluation with qualitative constraint networks of Interval Algebra.

Cite as

Michael Sioutis, Anastasia Paparrizou, and Jean-François Condotta. Collective Singleton-Based Consistency for Qualitative Constraint Networks. In 24th International Symposium on Temporal Representation and Reasoning (TIME 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 90, pp. 19:1-19:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)


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@InProceedings{sioutis_et_al:LIPIcs.TIME.2017.19,
  author =	{Sioutis, Michael and Paparrizou, Anastasia and Condotta, Jean-Fran\c{c}ois},
  title =	{{Collective Singleton-Based Consistency for Qualitative Constraint Networks}},
  booktitle =	{24th International Symposium on Temporal Representation and Reasoning (TIME 2017)},
  pages =	{19:1--19:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-052-1},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{90},
  editor =	{Schewe, Sven and Schneider, Thomas and Wijsen, Jef},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2017.19},
  URN =		{urn:nbn:de:0030-drops-79237},
  doi =		{10.4230/LIPIcs.TIME.2017.19},
  annote =	{Keywords: Qualitative constraint network, qualitative spatial and temporal reasoning, partial singleton path-consistency, local consistency, minimal labeling pr}
}