Datalog+/-: Questions and Answers

• What is Datalog± and what are its advantages? Datalog± is a rule-based formalism that combines the advantages of logic programming in Datalog with features for expressing ontological knowledge and advanced data modeling constraints. Datalog± provides a uniform framework for query answering and reasoning with incomplete data. It generalizes disparate other KR formalisms such as plain Datalog, description logics (DLs), in particular, DL-Lite and EL, F-Logic Lite, highly relevant fragments of UML class diagrams, data-exchange formalisms, graph query languages such as SPARQL, and so on. Datalog± is a conceptually very simple and clear cut formalism that extends plain Datalog with features such as existential quantifiers, equalities, and the falsum (⊥) in rule heads and, at the same time, restricts the rule syntax so as to achieve decidability and, when required, tractability. Its closeness to logic programming allowed us to enrich it by non-monotonic negation under the stratified, well-founded, and stable model semantics.