The LSV seminar takes place on Tuesday at 11:00 AM. The usual location is the conference room at Pavillon des Jardins (venue). If you wish to be informed by e-mail about upcoming seminars, please contact Stéphane Le Roux and Matthias Fuegger.
The seminar is open to public and does not require any form of registration.
The talk will present and relate results from two different papers:
The first paper provides complete axiomatizations of fragments of MSO on finite node-labelled sibling-ordered trees. In order to prove completeness, model-theoretic tools specifically geared towards Henkin models are developed (e.g. Ehrenfeucht-Fraïssé games and Feferman-Vaught theorems).
The second paper studies the data and combined complexity of query answering over incomplete XML documents, completing the picture of previous studies by examining more expressive languages and other semantic assumptions. A new tractable class of FO queries is identified both for the relational and XML case: Boolean combinations of existential positive queries (under open and closed world assumptions). The results are obtained via a new technique which has a model-theoretic flavor, whereas automata-theoretic techniques are usually predominant in the study of XML.
I will take the occasion to emphasize and discuss the use of model-theoretic techniques in the study of logics on trees.