DLV-HEX: Dealing with Semantic Web under Answer-Set Programming

We present an implementation of HEX programs, which are nonmonotonic logic programs admitting higher-order atoms as well as external atoms. Higher-order features are widely acknowledged as useful for various tasks, including meta-reasoning. Furthermore, the possibility to exchange knowledge with external sources in a fully declarative framework such as answer-set programming (ASP) is nowadays important, in particular in view of applications in the Semantic-Web area. Through external atoms, HEX programs can deal with external knowledge and reasoners of various nature, such as RDF datasets or description-logic knowledge bases.