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This chapter provides an introduction to Description Logics as a formal language for representing knowledge and reasoning about it. It first gives a short overview of the ideas underlying Description Logics. Then it introduces syntax and semantics, covering the basic constructors that are used in systems or have been introduced in the literature, and the(More)
We have developed and implemented the Relational Grid Monitoring Architecture (R-GMA) as part of the DataGrid project, to provide a flexible information and monitoring service for use by other middleware components and applications. R-GMA presents users with a virtual database and mediates queries posed at this database: users pose queries against a global(More)
We study the problem of evolution for Knowledge Bases (KBs) expressed in Description Logics (DLs) of the DL-Lite family. DL-Lite is at the basis of OWL 2 QL, one of the tractable fragments of OWL 2, the recently proposed revision of the Web Ontology Language. We propose some fundamental principles that KB evolution should respect. We review known model and(More)
ur K ¨ unstliche In-telligenz, DFKI) with sites in Kaiserslautern and Saarbrücken is a non-profit organization which was founded in 1988. The DFKI conducts application-oriented basic research in the field of artificial intelligence and other related subfields of computer science. The overall goal is to construct systems with technical knowledge and common(More)
We present two concept languages,, called PL 1 and PL 2 which are extensions of TC-. We prove that the subsumption problem in these languages can be solved in polynomial time. Both languages include a construct for expressing inverse roles, which has not been considered up to now in tractable languages. In addition, PL 1 includes number restrictions and(More)
Equivalence of aggregate queries is investigated for the class of conjunctive queries with comparisons and the aggregate operators count, count-distinct, min, max, and sum. Essentially, this class contains unnested SQL queries with the above aggregate operators, with a where clause consisting of a conjunction of comparisons, and without a having clause. The(More)
We investigate the use of epistemic operators in the framework of concept languages (also called terminological languages). The results of this work have a twofold signiicance. From the point of view of epistemic logics, our contribution is to have identiied an effective procedure for the problem of answering epistemic queries posed to a knowledge base(More)