| Links' Seminars and Public Events |   |
| 2017 | |
|---|---|
Fri 20th Jan 10:30 am 12:30 pm | 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.  Inria Lille |
Wed 11th Jan 2:15 pm 3:25 pm | 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. Lille B21 |
Mon 9th Jan to Fri 13th Jan all day | Visite Michael vanden Boom, Oxford University |
| 2016 | |
Fri 9th Dec all day | Kickoff Headwork Paris MNHN |
Fri 18th Nov 10:30 am 12:00 pm | Florent Capelli Links Seminar "Lille-Salle B21" |
Fri 18th Nov all day | Florent Capelli visit |
Tue 8th Nov 2:30 pm 4:30 pm | 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 | PhD defense Adrien Boiret |
Fri 4th Nov all day | colis general meeting Paris |
Thu 27th Oct 10:00 am 6:00 pm | Links day |
Thu 27th Oct all day | links day |
Thu 20th Oct 2:00 pm 4:00 pm | 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 5:30 pm | comité de projet |
Thu 13th Oct 2:00 pm 3:00 pm | Seminar Christof Löding "Lille-Salle B21" |
Thu 13th Oct to Fri 14th Oct all day | visit christof löding |
