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A. Pieris:
"Default Negation for Datalog+/-";
Keynote Lecture: Workshop on Grounding and Transformations for Theories With Variables (GTTV), Lexington, KY, USA (invited); 2013-09-15.

The Datalog+/- family of expressive extensions of Datalog has recently been introduced as a new paradigm for query answering in the presence of ontologies. It extends plain Datalog by features such as existential quantification in rule-heads and, at the same time, restricts the rule syntax so as to achieve decidability and tractability w.r.t. the dataset. Although the obtained formalisms are expressive enough for capturing standard ontology languages based on description logics, they are not powerful enough for expressing default negation (a.k.a. negation as failure).
The database and the KR communities have recognized the need for extending Datalog+/- with default negation. Adding negation to existing Datalog+/- languages is an intriguing new problem that gave rise to a flourishing research activity the last years. In this talk, we are going to give an overview of recent results on conjunctive query answering under the main Datalog+/- languages enriched with negation, focussing on the well-founded and stable model semantics.