Seminars

Links' Seminars and Public Events Add to google calendar
2017
Fri 10th Nov
10:00 am
11:00 am
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Momar Sakho: "Complexity of Certain Query Answering on Hyperstreams"
A hyperstream is a sequence of streams with references to others. We study the complexity of computing certain answers for queries defined by automata and evaluated on hyperstreams of words. We show that the problem is PSPACE-complete for deterministic query automata, but that it can be solved in PTime for linear hyperstreams even with factorization.
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Salle B21
Fri 3rd Nov
10:30 am
12:00 pm
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Joanna Ochremiak, Paris 7: "Proof complexity of constraint satisfaction problems"
Many natural computational problems, such as satisfiability and
systems of equations, can be expressed in a unified way as constraint
satisfaction problems (CSPs). In this talk I will show that the usual
reductions preserving the complexity of the constraint satisfaction
problem preserve also its proof complexity. As an application, I will
present two gap theorems, which say that CSPs that admit small size
refutations in some classical proof systems are exactly the constraint
satisfaction problems which can be solved by Datalog.

This is joint work with Albert Atserias.

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B21
Fri 13th Oct
11:00 am
1:00 pm
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Dimitri Gallois: On parallel rewriting
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B21
Fri 29th Sep
10:00 am
12:00 pm
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Nicolas Bacquey: "An algorithm for deciding the equivalence of tree transducers"
As an extension of word transformations, tree transformations have numerous applications in computer science : XSLT transformations, Unix packages installation and removal, databases queries... Likewise, there are many formal models to describe these transformations. However, the proof of formal properies on these models is often difficult, or even undecidable.
In this talk, I will be interested in one of the simplest model for tree transformations, namely deterministic top-down tree transducers (DTOP). It has been known for a while that the equivalence problem of DTOPs can be solved via an earliest normal form comparison algorithm, that is in 2EXPTIME. However, when applying this algorithm to practical cases, it seemed that the worst case was not bound to happen often, if ever.
I will present a new algorithm for the problem, based on the search of counterexamples via the expansion and unification of a set of rules over states of DTOPs. The most interesting feature of this algorithm is that it runs in exponential time, thus proving that the equivalence problem of DTOPs is in fact EXPTIME-complete.

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Lille B31
Thu 6th Jul
 all day
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ANR Headwork: General Meeting
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Rennes
Fri 16th Jun
 all day
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09h15-09h45 Coffee Welcome
09h45-10h30 Michel de Rougemont: Approximate integration of streaming graph edges
10h30-11h15 Florent Cappelli: Understanding the complexity of #SAT using knowledge compilation
11h15-11h45 Yann Strozecki: Enumerating maximal solutions of saturation problems
12h00 Lunch
14h00 Discussion libre
16h00 End
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Inria Lille
Thu 15th Jun
 all day
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09h15-09h45 Welcome coffee
09h45-10h30 Pierre Bourhis: Introduction of circuit from database queries
10h30-11h15 Jen Keppeler: Answering FO+MOD queries under updates on bounded degree databases
11h15-12h00 Antoine Amarilli: Enumeration of valuation of circuits
12h00-13h30 Lunch + Café
13h30-14h30 Jan Ramon: Question around IA
14h30-15h15 Ahmet Kara: Covers of Query Results
15h15-15h45 Break
15h45-16h30 Alexandre Vigny: Constant delay enumeration for FO queries over
databases with local bounded expansion

20h00 Dinner at Le Palermo
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Inria Lille
Fri 9th Jun
10:30 am
12:30 pm
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Valentin Montmirail: "A Recursive Shortcut for CEGAR: Application to the Modal Logic K Satisfiability Problem"
Counter-Example-Guided Abstraction Refinement (CEGAR) has been very successful in model checking.
Since then, it has been applied to many different problems. It is especially proved to be a highly successful practical approach for solving the PSPACE complete QBF problem. In this paper, we propose a new CEGAR-like approach for tackling PSPACE complete problems that we call RECAR (Recursive Explore and Check Abstraction Refinement). We show that this generic approach is sound and complete. Then we propose a specific implementation of the RECAR approach to solve the modal logic K satisfiability problem. We implemented both CEGAR and RECAR approaches for the modal logic K satisfiability problem within the solver MoSaiC. We compared experimentally those approaches to the state-of-the-art solvers for that problem. The RECAR approach outperforms the CEGAR one for that problem and also compares favorably against the state-of-the-art on the benchmarks considered.
"Lille-Salle B21"
Tue 6th Jun
to Fri 9th Jun
 all day
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Visit of Jean-Marc Talbot, Université de Marseille

Fri 2nd Jun
 all day
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Visit of Floris Geerts, University of Antwerp
Fri 21st Apr
 all day
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Visit of Florent Capelli, London University
Fri 24th Mar
 all day
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Visit of Charles Paperman, Université Paris 7
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INRIA Institut National Recherche Informatique Automatique
40 Avenue Halley, 59650 Villeneuve d'Ascq, France
Wed 15th Mar
10:30 am
12:00 pm
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Emmanuel Filliot, Université Libre de Bruxelles: "Automata, Logic and Algebra for Word Transductions"

This talk will survey old and recent results about word transductions, i.e. functions mapping (finite) words to words. Connections between automata models (transducers), logic and algebra will be presented. Starting with rational functions, defined by (one-way) finite transducers, and the canonical model of bimachines introduced by Reutenauer and Schützenberger, the talk will also target the more expressive class of functions defined by two-way transducers and their equivalent MSO-based formalism.

"Lille-Salle B21"
Wed 15th Mar
 all day
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Visit of Emmanuel Filliot, Université Libre de Bruxelles

Wed 1st Feb
11:00 am
12:30 pm
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Pierre Bourhis: The Chase
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Inria Lille
Fri 20th Jan
10:30 am
12:30 pm
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Pierre Bourhis: "Tree Automata for Reasoning in Databases and Artificial Intelligence"
In database management, one of the principal task is to optimize the queries to evaluate them efficiently. It is in particular the case for recursive queries for which their evaluation can lead to crawl all the database. In particular, one of the main question is to minimize the queries in order to avoid to evaluate useless parts of the query. The core theoretical question around this line of work is the problem of inclusion of a query in another. Interestedly, this question is related to an important question in IA which is to answer a query when the data is incomplete but rules are given to derive new information. This problem is called certain query answering. In both context, if both problem are undecidable in general, there are fragments based on guardedness that are decidable due to the fact there exists witness of the problems that have a bounded tree width and that their encoding in trees is regular. Furthermore, the queries can be translated in MSO. In both contexts, Courcelle’s Theorems imply the decidability of both problems. I will present to the different results on the translation of logic class of formula for our problems into tree automata to obtain tight bounds to the problems of inclusion of recursive queries or certain query answering.

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Inria Lille
Wed 11th Jan
2:15 pm
3:25 pm
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Michael vanden Boom, Oxford University : Decidable fixpoint logics
Fixpoint logics can express dynamic, recursive properties, but often fail to have decidable satisfiability. A notable exception to this is the family of well-behaved "guarded" fixpoint logics,
which subsume a variety of query languages and integrity constraints of interest in databases and knowledge representation. In this talk, I will survey some recent results about these logics.
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Lille B21
Mon 9th Jan
to Fri 13th Jan
 all day
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Visite Michael vanden Boom, Oxford University
2016
Fri 9th Dec
 all day
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Kickoff Headwork
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Paris MNHN
Fri 18th Nov
10:30 am
12:00 pm
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Florent Capelli Links Seminar
"Lille-Salle B21"
Fri 18th Nov
 all day
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Florent Capelli visit
Tue 8th Nov
2:30 pm
4:30 pm
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Seminar Link by Helmut Seidl: "Equivalence of Deterministic Top-Down Tree-to-String Transducers is Decidable"
Abstract:

We show that equivalence of deterministic top-down tree-to-string transducers is decidable,
thus solving a long standing open problem in formal language theory.
We also present efficient algorithms for subclasses:
polynomial time for total transducers with unary output alphabet (over a given top-down regular domain language),
and co-randomized polynomial time for linear transducers, these results are obtained using techniques from multi-linear algebra.
For our main result, we prove that equivalence can be certified by means of inductive invariants using polynomial ideals.
This allows us to construct two semi-algorithms, one searching for a proof of equivalence, one for a witness of non-equivalence.
"Lille-Salle B31 "
Mon 7th Nov
2:00 pm
4:00 pm
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PhD defense Adrien Boiret
Fri 4th Nov
 all day
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colis general meeting
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Paris
Thu 27th Oct
10:00 am
6:00 pm
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Links day
Thu 27th Oct
 all day
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links day
Thu 20th Oct
2:00 pm
4:00 pm
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Seminar Links by Vincent Hugot: "Top-Down Transducers for Data Trees"
Abstract:
Tree transducers have a wide range of application domains ranging from compiler construction,
program analysis, and computational linguistics, to semi-structured databases and file system
transformations. A common application of these domains is to specify and verify transformations
of data trees, i.e., trees whose nodes are labeled by data values from an infinite domain. Most
existing classes of tree transducers and their formal studies, however, are restricted to trees over
finite signatures without data. In this paper, we lift the most prominent class of top-down tree
transducers to data trees, such that its good properties are preserved. In particular, we show that
top-down transducers for data trees have a decidable equivalence problem, without imposing any
linearity restriction as in previous approaches based on symbolic top-down tree transducers.
"Lille-Salle B21"
Thu 13th Oct
2:00 pm
3:00 pm
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Seminar Christof Löding
"Lille-Salle B21"
Thu 13th Oct
2:00 pm
5:30 pm
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comité de projet
Thu 13th Oct
to Fri 14th Oct
 all day
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visit christof löding
Fri 30th Sep
 all day
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arrivée de Jose Lozano

Thu 29th Sep
2:00 pm
4:00 pm
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Seminar Links by Aurélien Lemay

"Lille-Salle B21"
Tue 27th Sep
 all day
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Ircica fetes ces 10 ans
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Lille
Fri 9th Sep
2:00 pm
4:00 pm
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Momar Sakho
"Lille-Salle B21"
Wed 7th Sep
11:00 am
12:00 pm
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jason demagoj

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