Séminaire LIMOS - 25 juin 2020 - Ontology-Mediated Query Answering in OWL 2 QL: Succinctness and Complexity Landscapes
Presenter : Meghyn Bienvenu, CR CNRS, LaBRI research lab at the University of Bordeaux
Abstract : Recent years have seen an increasing interest in ontology-mediated query answering (OMQA), in which the semantic knowledge provided by an ontology is exploited when querying data. One popular ontology language for OMQA is OWL 2 QL, a W3C-standardized language based upon the DL-Lite description logic. This language has the desirable property that OMQA can be reduced to database query evaluation by means of query rewriting. In this talk, I will consider two fundamental questions about OMQA with OWL 2 QL ontologies: 1) Is it possible to devise query rewriting algorithms that produce polynomial-size rewritings? 2) How does the worst-case complexity of OMQA vary depending on the structure of the ontology-mediated query (OMQ)? After classifying OMQs according to the shape of their conjunctive queries (treewidth, the number of leaves) and the existential depth of their ontologies, I will present the obtained complexity and succinctness landscapes and sketch some of the main ingredients in the proofs (in particular, a novel connection between OMQ rewritings and circuit complexity). 
This talk is based upon a JACM'18 paper co-authored with Stanislav Kikot, Roman Kontchakov, Vladimir Podolskii, and Michael Zakharyaschev.
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Vendredi 10 Juillet 2020
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