We tackle a long-standing open research problem and prove the decidability of query answering under the stable model semantics for guarded existential rules, where rule bodies may contain negated atoms, and provide complexity results. The results extend to guarded Datalog /- with negation, and thus provide a natural and decidable stable model semantics to description logics such as ELHI and DL-LiteR.

We provide a sound and complete axiomatization for a class of logics appropriate for reasoning about the rationality of players in games. Essentially the same axiomatization applies to a wide class of decision rules.

We examine several belief change operations in the light of Dynamic Logic of Propositional Assignments DL-PA. We show that we can encode in a systematic way update operations (such as Winslett's Possible Models Approach') and revision operations (such as Dalal's) as particular DL-PA programs. Every DL-PA formula being equivalent to a boolean formula, we obtain syntactical counterparts for all these belief change operations.

The paper addresses how the information state of an agent relates to the arguments that the agent endorses. Information states are modeled in doxastic logic and arguments by recasting abstract argumentation theory in a modal logic format. The two perspectives are combined by an application of the theory of product logics, delivering sound and complete systems in which the interaction of arguments and beliefs is investigated.

Today's propositional satisfiability (SAT) solvers are extremely powerful and can be used as an efficient back-end for solving NP-complete problems. However, many fundamental problems in knowledge representation and reasoning are located at the second level of the Polynomial Hierarchy or even higher, and hence polynomial-time transformations to SAT are not possible, unless the hierarchy collapses. Recent research shows that in certain cases one can break through these complexity barriers by fixed-parameter tractable (fpt) reductions which exploit structural aspects of problem instances in terms of problem parameters. In this paper we develop a general theoretical framework that supports the classification of parameterized problems on whether they admit such an fpt-reduction to SAT or not.

In the past, there have been several attempts to explain logic programming under the well-founded semantics as a logic of inductive definitions. A weakness in all is the absence of an obvious connection between how we understand various types of informal inductive definitions in mathematical text and the complex mathematics of the well-founded semantics. We formalize the induction process in the most common principles and prove that the well-founded model construction generalizes them all.

Sponsors

The tutorials presented at the Fourteenth International Conference on Principles of Knowledge Representation and Reasoning included Verification of Multi-Agent Systems against Epistemic Specifications by Alessio Lomuscio, Dynamic Epistemic Logic and Its Interaction with Knowledge Representation by Lawrence S. Moss, Natural Language Understanding with World Knowledge and Inference by Ekaterina Ovchinnikova, and Query Answering and Rewriting in Ontology-Based Data Access by Riccardo Rosati.

The invited talks presented at the Fourteenth International Conference on Principles of Knowledge Representation and Reasoning included Ontology-Based Monitoring of Dynamic Systems by Franz Baader, Knowledge Representation Meets Computer Vision: From Pixels to Symbolic Activity Descriptions by Tony Cohn, Datalog /–: Questions and Answers by Georg Gottlob, and Situation Calculus: The Last 15 Years by Sheila McIlraith.

In the summer of 2014, Vienna hosted the largest scientific conference in the history of logic. The Vienna Summer of Logic consisted of twelve large conferences and 82 workshops, attracting more than 2,000 researchers from all over the world. This unique event was organized by the Kurt Gödel Society at Vienna University of Technology and held from July 9 to 24, 2014, under the auspices of the Federal President of the Republic of Austria, Dr. Heinz Fischer.