Section: New Results

Ontology networks

Dealing with the semantic web, we are interested in ontology networks, i.e., sets of distributed ontologies that have to work together. One way for these systems to interact consists of exchanging queries and answers. For that reason, we pay particular attention to query systems.

Querying the semantic web is mainly done through the sparql language [18] . We designed one of its extensions, Psparql (Path sparql ) which provides queries with paths of arbitrary length. We continue this work by connecting it to the work of the wam team on static analysis of XPath expressions. More specifically, we consdider query contrainment, i.e., determining whether, for any graph, the answers to a query are contained in those of another query. This is achieved by reducing this problem to satisfiability in the $\mu$-calculus. In this work, rdf graphs are considered as transition systems and important fragments of rdfs and sparql as propositional $\mu$-calculus formulas. It is then possible to use solvers of this logic to test query containment of sparql queries under rdfs and owl schema constraints [11] , with paths or under particular entailment regimes [10] . We have also implemented the proposed techniques and provided a first benchmark for query containment available under http://sparql-qc-bench.inrialpes.fr .

This work is part of the PhD of Melisachew Wudage Chekol [4] , co-supervised with Nabil Layaïda (wam ).