Reifying Concepts in Description Logics

Abstract

Practical applications of description logics (DLs) in knowledge-based systems have forced us to introduce the following features which are absent from existing DLs: • allowing a concept to be regarded at the same time as an individual (the instance of some other meta-level concept) • allowing an individual to represent a co llection (set) of other individuals. The first extension, called concept reification , is more general and thus can cover the second one too. We argue that the absence of these features from existing DLs is an important reason for the lack of a unified approach to description logics and object-oriented databases. We also show that concept reification cannot be dealt with by the standard DL semantics and propose a slightly modified semantics that takes care of the inherent higher-order features of reification in a first-order setting . A sound and complete inference algorithm for checking consistency in reified A..CCOE knowledge bases is subsequently put forward .