Concept Projection in Algebras for Computing Certain Answer Descriptions

We introduce a projection operator over concepts in a given description logic that produces least subsumers of concepts in a language fragment that satisfies additional syntactic requirements specified as a parameter of the operator. The operator complements existing operators for concept selection and concept ordering that have been proposed in earlier work [3, 4]. We show how, altogether, the operators can form the basis of an algebra for computing more informative and user friendly varieties of certain answers over what we call a description base. This is a description logic (DL) knowledge base in which the ABox is replaced by a fixed and finite collection of arbitrary concepts. In the sections that follow, we introduce the notion of a description base, of a certain answer description over a description base and then present an algebra for computing a simple variety of certain answer descriptions that incorporates the new projection operator. We elaborate on the semantics of this operator, in particular the notion of a projection description, in the remaining sections of the paper where we consider the operator’s semantics as well as methods for efficient evaluation. In the final section, we outline a motivating example and suggest useful ways in which both projection descriptions and our query algebra might be extended.