Technical University of Dresden
Query Rewriting under Existential Rules
There is a clear consensus that the required level of scalability in ontology-mediated querying (OMQ) can only be achieved via query rewriting, a prominent tool that allows us to exploit standard database technology for OMQ purposes. The key idea is to reduce the problem in question to the problem of evaluating a first-order (FO)query over a relational database. This technique was originally proposed in 2005 in the context of DL-Lite. Since then it has been extensively applied, not only to more expressive DLs but also to existential rules (a.k.a. tuple-generating dependencies and Datalog+/- rules). This talk is about query rewriting under the main decidable classes of existential rules. The first part of the talk will focus on pure FO-rewritability, where the rewriting process is database independent. For the classes of existential rules that always admit FO-rewritings, I will present algorithms for constructing such rewritings and discuss their practical relevance. For the classes that do not always admit FO-rewritings, I will discuss the challenging problem of deciding whether a rewriting exists. In view of the fact that the above (pure) FO-rewritings are unavoidably very large, the second part of the talk will focus on combined FO-rewritability, a technique that allows us to construct small rewritings at the price of touching the database (but in a controlled way). In both parts of the talk, I will try to emphasize how query rewriting under DLs has influenced query rewriting under existential rules (and vice versa).
Brief Author Biography:
Andreas Pieris is a Lecturer in the School of Informatics at the University of Edinburgh. Prior to this, he was a postdoctoral researcher at the Institute of Information Systems of the Vienna University of Technology, and a postdoctoral researcher at the Department of Computer Science of the University of Oxford. His research interests are database theory with emphasis on query languages, knowledge representation and reasoning, and computational logic and its applications to computer science. His current work mostly focuses on theoretical and practical aspects of query answering in the presence of ontologies. He has published more than sixty papers, many of them in leading international conferences and journals. He has served on the PCs of numerous international conferences and workshops, including the top-tier database and AI conferences.
Ulrike Sattler (30th anniversary talk)
University of Manchester