Abstract
Knowledge representation and reasoning on the Semantic Web has recently focused, due to practical rationale, on the subset of first order logic called existential rules. In this thesis we investigate reasoning with existential rules in presence of conflicting information and introduce defeasible existential rule reasoning. We provide three main salient results as follows. First we show that classical defeasible reasoning techniques need to be revisited for existential rules and study their theoretical and implementation related challenges. Second, we provide a new combinatorial structure that allows for diverse variants of defeasible reasoning to be captured together and study its expressivity and versatility. Third we evaluate our work with respect to the state of the art in inconsistency handling in existential rules and investigate the human appeal of such reasoning techniques.