Abstract:Based on the vision of the Semantic Web, DLclog, a new hybrid formalism combining description logics (DL) and logic programming (LP), is described, which extends DL+log from syntax and semantics. In DLclog, negative dl-atoms can occur in the bodies of the rules, and are interpreted non-classically by McCarthy’s parallel circumscription, i.e., the extents of these DL predicates are minimized with the extents of all other DL predicates varying. In this way, the Nonmonotonic Semantics (NM-Semantics) of DL+log is extended to the Nonmonotonic Circumscriptive Semantics (NMC-Semantics), and therefore, DLclog becomes the hybrid system with the stronger expressiveness and reasoning abilities. A decision procedure is given when DL ontology is written in ALCIO or ALCQO and roles are not allowed to occur in negative dl-atoms, and the complexity is analyzed.