CNRS Lens Computer Science Research Center

Artois, France

CNRS Lens Computer Science Research Center

Artois, France

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Chen H.,University of the Basque Country | Chen H.,Ikerbasque | Mengel S.,CNRS Lens Computer Science Research Center
Proceedings of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems | Year: 2016

Existential positive formulas form a fragment of first-order logic that includes and is semantically equivalent to unions of conjunctive queries, one of the most important and well-studied classes of queries in database theory. We consider the complexity of counting the number of answers to existential positive formulas on finite structures and give a trichotomy theorem on query classes, in the setting of bounded arity. This theorem generalizes and unifies several known results on the complexity of conjunctive queries and unions of conjunctive queries. We prove this trichotomy theorem by establishing a result which we call the equivalence theorem, which shows that for each class of existential positive formulas, there exists a class of conjunctive queries having the same complexity (in a sense made precise). © 2016 ACM.


Lecoutre C.,CNRS Lens Computer Science Research Center | Paparrizouy A.,University of Western Macedonia | Stergiou K.,University of Western Macedonia
Proceedings of the 27th AAAI Conference on Artificial Intelligence, AAAI 2013 | Year: 2013

One of the most widely studied classes of constraints in constraint programming (CP) is that of table constraints. Numerous specialized filtering algorithms, enforcing the well-known property called generalized arc consistency (GAC), have been developed for such constraints. Among the most successful GAC algorithms for table constraints, we find variants of simple tabular reduction (STR), like STR2. In this paper, we propose an extension of STR-based algorithms that achieves full pairwise consistency (FPWC), a consistency stronger than GAC and max restricted pairwise consistency (maxRPWC). Our approach involves counting the number of occurrences of specific combinations of values in constraint intersections. Importantly, the worst-case time complexity of one call to the basic filtering procedure at the heart of our new algorithm is quite close to that of STR algorithms. Experiments demonstrate that our method can outperform STR2 in many classes of problems, being significantly faster in some cases. Also, it is clearly superior to maxRPWC+, an algorithm that has been recently proposed. Copyright © 2013, Association for the Advancement of Artificial Intelligence (www.aaai.org). All rights reserved.


Benferhat S.,University of Lille Nord de France | Benferhat S.,University of Artois | Benferhat S.,CNRS Lens Computer Science Research Center
Artificial Intelligence | Year: 2010

Causality and belief change play an important role in many applications. This paper focuses on the main issues of causality and interventions in possibilistic graphical models. We show that interventions, which are very useful for representing causal relations between events, can be naturally viewed as a belief change process. In particular, interventions can be handled using a possibilistic counterpart of Jeffrey's rule of conditioning under uncertain inputs. This paper also addresses new issues that are arisen in the revision of graphical models when handling interventions. We first argue that the order in which observations and interventions are introduced is very important. Then we show that in order to correctly handle sequences of observations and interventions, one needs to change the structure of possibilistic networks. Lastly, an efficient procedure for revising possibilistic causal trees is provided. © 2009 Elsevier B.V. All rights reserved.


Raddaoui B.,CNRS Lens Computer Science Research Center
ICAART 2015 - 7th International Conference on Agents and Artificial Intelligence, Proceedings | Year: 2015

Measuring the degree of conflict of a knowledge base can help us to deal with inconsistencies. Several semantic and syntax based approaches have been proposed separately. In this paper, we use logical argumentation as a field to compute the inconsistency measure for propositional formulae. We show using the complete argumentation tree that our family of measures is able to express finely the inconsistency of a formula following their context and allows us to distinguish between formulae. We extend our measure to quantify the degree of inconsistency of set of formulae and give a general formulation of the inconsistency using some logical properties.


Benferhat S.,CNRS Lens Computer Science Research Center | Bouraoui Z.,CNRS Lens Computer Science Research Center
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2013

DL-Lite is one of the most important fragment of description logics that allows a flexible representation of knowledge with a low computational complexity of the reasoning process. This paper investigates an extension of DL-Lite to deal with uncertainty associated with objects, concepts or relations using a possibility theory framework. Possibility theory offers a natural framework for representing uncertain and incomplete information. It is particularly useful for handling inconsistent knowledge. We first provide foundations of possibilistic DL-Lite, denoted by π-DL-Lite, where we present its syntax and its semantics. We then study the reasoning tasks and show how to measure the inconsistency degree of a knowledge base using query evaluations. An important result of the paper is that the extension of the expressive power of DL-Lite is done without additional extra computational costs. © 2013 Springer-Verlag Berlin Heidelberg.


Jabbour S.,CNRS Lens Computer Science Research Center | Raddaoui B.,CNRS Lens Computer Science Research Center
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2013

Measuring the degree of inconsistency of a knowledge base provides important context information for making easier inconsistency handling. In this paper, we propose a new fine-grained measure to quantify the degree of inconsistency of propositional formulae. Our inconsistency measure uses in an original way the minimal proofs to characterize the responsibility of each formula in the global inconsistency. We give an extension of such measure to quantify the inconsistency of the whole base. Furthermore, we show that our measure satisfies the important properties characterizing an intuitive inconsistency measure. Finally, we address the problem of restoring consistency using an inconsistency measure. © 2013 Springer-Verlag Berlin Heidelberg.


Mengel S.,CNRS Lens Computer Science Research Center
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2016

We show unconditional parameterized lower bounds in the area of knowledge compilation, more specifically on the size of circuits in decomposable negation normal form (DNNF) that encode CNF-formulas restricted by several graph width measures. In particular, we show that - there are CNF formulas of size n and modular incidence treewidth k whose smallest DNNF-encoding has size nΩ (k), and - there are CNF formulas of size n and incidence neighborhood diversity k whose smallest DNNF-encoding has size nΩ (√k). These results complement recent upper bounds for compiling CNF into DNNF and strengthen-quantitatively and qualitatively-known conditional lower bounds for cliquewidth. Moreover, they show that, unlike for many graph problems, the parameters considered here behave significantly differently from treewidth. © Springer International Publishing Switzerland 2016.


Gharbi N.,CNRS Lens Computer Science Research Center
Proceedings - International Conference on Tools with Artificial Intelligence, ICTAI | Year: 2016

In the latest years and with the advancements of the multicore computing world, the constraint programming community tried to benefit from the capacity of new machines and make the best use of them through several parallel schemes for constraint solving. In this paper, we present a new approach using parallel consistencies to enhance the classical solving process. Specifically, we propose an approach where a master process tries to solve a constraint satisfaction problem while using the results of consistency tests done by auxiliary workers so as to avoid some useless branching. © 2015 IEEE.


Gregoire E.,CNRS Lens Computer Science Research Center
Proceedings of the 2014 IEEE 15th International Conference on Information Reuse and Integration, IEEE IRI 2014 | Year: 2014

We propose and experiment a practical multi-level approach to maintain contradiction-free knowledge when some incoming additional information that can contradict the preexisting knowledge must be taken into account. The approach implements an any-time strategy that triggers successive reasoning paradigms ranging from credulous to computationally more intensive forms of skepticism about conflicting information. It makes use of recent dramatic computational progress in constraint satisfaction techniques for finite domains and Boolean-related search and reasoning. © 2014 IEEE.


Mailly J.-G.,CNRS Lens Computer Science Research Center
IJCAI International Joint Conference on Artificial Intelligence | Year: 2013

My thesis work aims to study change operations for argumentation systems, especially for abstract argumentation systems à la Dung. This paper presents a first study of the AGM revision adapted to the case of argumentation. We also sketch future research works planned to complete the one already achieved.

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