Seminars

Links' Seminars and Public Events Add to google calendar
2018
Fri 26th Oct
11:00 am
12:30 pm
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Momar Sakho in Links seminar
"Lieu : Lille, Salle : A12"
Thu 18th Oct
4:00 pm
5:00 pm
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Talk of Mikael Monet
Title: Combined Complexity of Probabilistic Query Evaluation

Abstract:
Query evaluation over probabilistic databases (probabilistic query evaluation, or PQE) is known to be intractable in many cases, even in data complexity, i.e., when the query is fixed. Although some restrictions of the queries and instances have been proposed to lower the complexity, these known tractable cases usually do not apply to combined complexity, i.e., when the query is not fixed. This talk gives an overview of my PhD research, which investigates which queries and instances ensure the tractability of PQE in combined complexity.

I will first present our work on PQE of conjunctive queries on binary signatures, which can be rephrased as a probabilistic graph homomorphism problem. We restrict the query and instance graphs to be trees and show the impact on the combined complexity of diverse features such as edge labels, branching, or connectedness. This is joint work with Antoine Amarilli and Pierre Senellart and was presented at PODS'2017.

Second, we will explore the combined complexity of evaluating queries on treelike databases, i.e., databases whose treewidth is bounded by a constant. We introduce a class of queries (named 'CFG-Datalog') which generalizes many known query languages that are tractable in this context. Specifically, we show that the (non-probabilistic) evaluation of CFG-Datalog on treelike databases can be solved with complexity linear in the product of the instance size and of the query size. In the process, we introduce a new representation of the provenance of a query on a database, based on cyclic Boolean circuits. This is joint work with Antoine Amarilli, Pierre Bourhis, and Pierre Senellart, and was presented at ICDT'2017.

Last, we will move to the field of knowledge compilation and present our work that connects various notions of width for Boolean circuits. We show that circuits of bounded treewidth can be efficiently compiled into structured deterministic decomposable normal forms (d-SDNNFs), which in particular allows efficient probability computation. We show the implications of this result for PQE of CFG-Datalog on treelike databases. We also prove general lower bounds on knowledge compilation formalisms, which imply lower bounds for provenance computation. This is joint work with Antoine Amarilli and Pierre Senellart and was presented at ICDT'2018.
"Lieu : Lille, Salle : B21"
Fri 28th Sep
10:15 am
11:45 am
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José Lozano Links seminar
Fri 21st Sep
10:30 am
12:00 pm
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Fabian Reiter in Links' Seminar: Descriptive distributed complexity
This talk connects two classical areas of theoretical computer science: descriptive complexity and distributed computing. The former is a branch of computational complexity theory that characterizes complexity classes in terms of equivalent logical formalisms. The latter studies algorithms that run in networks of interconnected processors.

Although an active field of research since the late 1970s, distributed computing is still lacking the analogue of a complexity theory. One reason for this may be the large number of distinct models of distributed computation, which make it rather difficult to develop a unified formal framework. In my talk, I will outline how the descriptive approach, i.e., connections to logic, could be helpful in this regard.
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Salle B21
Fri 7th Sep
11:00 am
12:30 pm
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Rustam Azimov in Links Seminar: "Context-Free Path Querying by Matrix Multiplication"
Fri 25th May
10:00 am
11:30 am
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Nicolas Crosetti in Links' Seminar: Dependency weighted aggregation
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Lille B21
Fri 27th Apr
10:30 am
12:30 pm
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Yann Strozecki in Links' Seminar: Methods in enumeration
In enumeration we are interested in generating a set of solutions, while bounding the time needed to generate one solution. We will first present the complexity measures used in this context, simple theoritical results and a few open questions.
We then introduce classical problems in this area such as the enumeration of: trees, models of a DNF, model of a FO or MSO formula, the maximal cliques of a graph, circuits of a matroid ...
We use them to illustrate the algorithmic toolbox of enumeration (Gray Code, backtrack search, reverse search, saturation...).
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Lille B21
Wed 25th Apr
2:15 pm
3:45 pm
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Nicolas Stage
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Jan's office
Fri 20th Apr
2:15 pm
3:45 pm
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Nicolas Stage
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Jan's office
Fri 13th Apr
2:15 pm
3:45 pm
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Nicolas Stage
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Jan's office
Fri 13th Apr
10:00 am
12:00 pm
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Iovka Boneva and Jérémie Dusart in Links' Seminar: Shape Expressions Schemas 2.0 : Semantics and Implementation
We will present the semantics of the ShEx language, its implementation
in java, and future directions of research.
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Salle B21
Fri 6th Apr
2:15 pm
3:45 pm
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Nicolas Stage
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Jan's office
Fri 30th Mar
2:15 pm
3:45 pm
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Nicolas Stage
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Jan's office
Fri 23rd Mar
10:00 am
11:30 am
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Paul Gallot: High-Order Tree Transducers
Paul présentera le papier de Sylvain, Aurélien et Paul, soumis à LICS 2018, sur le sujet des transducteurs d'arbres d'ordre supérieur.
Wed 21st Mar
2:00 pm
3:15 pm
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répétition Delta

Fri 16th Mar
10:00 am
11:30 am
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Luc Dartois in Links' Seminar: A Logic for Word Transductions with Synthesis
In this talk I present a logic, called LT, to express properties of transductions, i.e. binary relations from input to output (finite) words. I argue that LT is a suitable candidate as a specification language for verification of non reactive systems, extending the successful approach of verifying synchronous systems via Mealy Machines and MSO.

In LT, the input/output dependencies are modelled via an origin function which associates to any position of the output word, the input position from which it originates. LT is well-suited to express relations (which are not necessarily functional), and can express all regular functional transductions, i.e. transductions definable for instance by deterministic two-way transducers.
Despite its high expressive power, LT has decidable satisfiability problems. The main contribution is a synthesis result: it is always possible to synthesis a regular function which satisfies the specification.

Finally, I explicit a correspondence between transductions and data words. As a side-result, we obtain a new decidable logic for data words.
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Inria Lille
Fri 9th Mar
10:00 am
11:00 am
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Benjamin Bergougnoux : Counting minimal transversals of hypergraphs
A transversal of a hypergraph H is a subset of vertices that
intersects all the hyper-edges H. The enumeration and the counting of
the minimal transversals have a lot of applications in many domains
(graph theory, AI, datamining, etc). Counting problems are generally
harder than theirs associated decision problems. For example, finding
a minimal transversal is doable in polynomial time but counting them
is #P-complet (the equivalent of NP-complet for counting problems).

We have proved that we can count the minimal transversals of any
beta-acyclique hypergraph in polynomial time. Our result is based on
a recursive decomposition of the beta-acyclique hypergraph founded by
Florent Capelli and by the introduction of a new notion that
generalize the minimal transversals.

A lot of exciting open questions live in the neighborhood of our
result. In particular, our algorithm is able to count the minimum
dominating set of a strong-chordal graph. But counting the minimum
dominating set is #P-complete on split graphs. Is it the beginning of
a complete characterization of the complexity of counting minimal
dominating sets in dense graphs ?
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Salle B21

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