When : Tuesday July 21th
Where : Ecole Normale Superieure, Cachan, LSV Library
Agenda :
- Petrucio Viana (from Rio de Janeiro): algebras of binary relations and graph calculi
- Gaelle Fontaine (from Amsterdam): a characterization of the continuous fragment of the mu-calculus and/or an easy completeness proof for the mu-calculus on finite trees.
- Balder Ten Cate : on modal definability and universal Horn conditions.
Events
Dissemination, Workshop
Werner Nutt is visiting Webdam from Monday 20 April to Friday 24 April 2009. He is a professor at the Faculty of Computer Science at the Free University of Bozen-Bolzano.
He will present his work on containment of conjunctive queries over databases with null values Friday at 2:00pm in the meeting room G008.
Title : Containment of Conjunctive Queries over Databases with Null Values (Joint work with Carles Farre, Ernest Teniente, and Toni Urpi, UPC Barcelona)
Summary : Intuitively, one query “contains” another query if it is more general than the other query. Query containment is a key topic in database theory, which was originally motivated as a foundation of query optimisation, but has also other applications, such as integrity checking and information integration.
The containment problem has been studied for many different types of queries. The work so far, however, has never considered the effect of SQL style null values, although they are ubiquitous in real world data and queries have to process them.
In this talk we discuss in which ways null-containment, that is, containment in the presence of null values, differs from the non-null case. We consider conjunctive queries, which are essentially single block SQL queries. We show that null-containment, as in the non-null case, is NP-complete for boolean queries, which return only yes or no, while the situation becomes different from the classical case for queries that output data. We also discuss sufficient, but non-necessary criteria for null-containment, special cases with polynomial complexity, the effect of “is null” tests, as well as null-containment for richer classes of queries where comparisons or unions are allowed.
Short Bio : Werner Nutt is a professor at the Faculty of Computer Science at the Free University of Bozen-Bolzano in the Italian Alps (since 2005). He obtained a PhD and a habilitation from the university of Saarbruecken, was a visiting associate professor in Jerusalem (1997-2000) and a reader at Heriot-Watt University in Edinburgh (2000-2005). His research interests are in Artificial Intelligence and Databases, with a focus on Description Logics, Information Integration and Incomplete Information.
News
Database Theory, Visitors
Bruno Marnette is visiting Webdam Thursday 16 April 2009. He is a phD student at the computing laboratory of the Oxford University.
He will present his work on schema mappings Thursday at 10:30am at ENS Cachan in LSV-library.
Title : Schema-Mappings: From Termination To Tractability
Summary : Data-Exchange is the problem of creating automatically a new database while integrating the information encoded in (1) a given source database and (2) a high-level specification called schema-mapping. After investing the general properties of (generalised) schema-mappings and their semantics, I will introduce in this talk a new sufficient condition TOC for polynomial data-complexity. This criteria TOC generalizes strictly and substantially the best previously-known criteria called Weak-Acyclicity and relies on the termination of (a refinement of) a known procedure called Oblivious Chase. While TOC is RE-complete, I will finally present a more restrictive criteria SwA (for Super-weak Acylicity) that can be decided in polynomial time while generalizing already substantially the notion of Weak Acyclicity.
News
Database Theory, Visitors
Diego Calvanese is visiting Webdam from Monday 23 February to Friday 27 February 2009. He is a professor at the Faculty of Computer Science at the Free University of Bozen-Bolzano.
He will present his work on Ontology-Based Data Access and Data Integration Wednesday at 2:00pm in the meeting room N107.
Title : Ontology-Based Data Access and Data Integration
Summary :Ontologies provide a conceptualization of a domain of interest. Nowadays, they are typically represented in terms of Description Logics, and are seen as the key technology used to describe the semantics of information at various sites. The idea of using ontologies as a conceptual view over data repositories is becoming more and more popular. In order for this idea to become widespread in standard applications, it is fundamental that the conceptual layer through which the underlying data layer is accessed does not introduce a significant overhead in dealing with the data. Based on these observations, in recent years techniques to access data sources through a conceptual layer built on top of them have been developed, and the computational complexity of answering queries over ontologies, measured in the size of the underlying data, has been studied. In the talk we will present the general ideas underlying ontology based data access and integration, and will discuss the tradeoff between expressive power of the ontology language, and efficiency in query processing. Specifically, we will address the possibility of delegating query processing in ontology based data access to a relational database engine and will also present the QuOnto system, implementing this approach.
News
Database Theory, Ontologies, Visitors
When : Friday August 28th (just after VLDB)
Who : Webdam members and Webdam advisory board
Where : Telecom ParisTech, Paris [46, rue Barrault - 75013 Paris]
Agenda :
- Brainstorming session with all the members
- Private first meeting of the advisory board
Summary :
- What do we expect from foundations of Web data management?
- What are the goals?
- What should be the content?
- What can be achieved in Webdam?
Full program : see Workshop program
Notes on the meeting
Events
Dissemination, Workshop
This event has been cancelled.
Events
Dissemination, Workshop
Werner Nutt and Diego Calvanese from Free U. of Bozen-Bolzano will both come for short visits.
News
Visitors
After the first round of intensive recruitment all around the world, we are happy to announce and welcome the future new members of the project.
- Balder ten Cate from U. of Amsterdam will join us in April for 6 months and possibly more
- Yannis Katsis from UCSD will join us after his thesis around September for hopefully a long time.
- We are quite confident that Marie-Christine Rousset from U Grenoble and Philippe Rigaux from U. Paris Dauphine will join us for a long time.
Moreover, Evgeny Kharlamov, PhD student at the Free U. of Bozen-Bolzano is already visiting for 6 months: he is working with Serge A. and Pierre S. on aggregate functions for probabilistic databases. This is a joint work with Werner Nutt from the same university.
Of course, we are still looking for great researcher to join our project and we hope that is just a start!
News
Members
The Academy of Science of the Institut de France is a select group of French scholars joined by foreign scholars, all chosen from among the most eminent in their fields. Serge Abiteboul is one of eleven newly elected members.
The Academy of Science has various roles, from examining the standing worldwide of research carried out in France, to how research is organized and its interface with the public, seeking to ensure that scientific culture and the advancement of knowledge are accessible to everyone. It also plays an active part in the development of international relations between researchers and institutions, especially in Europe. Lastly, the Academy of Science, thanks to its multi-disciplinary approach and its interactions with other branches of knowledge, contributes, as part of the Institut de France, to the life and livelihood of science.
News
Awards
When : Friday January 9th
Who : By invitation only
Where : Ecole Normale Supérieure, Cachan, LSV Library
Agenda :
- 12:00-14:00 : lunch
- 14:00-15:00 : presentation of Webdam (Serge)
- 15:00-16:00 : brainstorming
Summary : slides of the presentation.
Events
Meetings
