A Formally Specified Ontology Management API as a Registry for Ubiquitous Computing Systems Alexander Paar 1 , Jürgen Reuter 1 John Soldatos 2 , Kostas Stamatis 2 , Lazaros Polymenakos 2 1 Institute for Program Structures and Data Organization, Universität Karlsruhe (TH), Am Fasanengarten 5, 76128 Karlsruhe, Germany alexpaar@acm.org, reuter@ipd.uka.de http://www.ipd.uka.de/Tichy 2 Athens Information Technology 19,5 km Markopoulou Peania, Ave. jsol@ait.edu.gr, ksta@ait.edu.gr, lcp@ait.edu.gr http://www.ait.edu.gr Abstract. Recently, several standards have emerged for ontology markup lan- guages that can be used to formalize all kinds of knowledge. However, there are no widely accepted standards yet that define APIs to manage ontological data. Processing ontological information still suffers from the heterogeneity imposed by the plethora of available ontology management systems. Moreover, ubiquitous computing environments usually comprise software components written in a variety of different programming languages, which makes it even more difficult to establish a common ontology management API with pro- gramming language agnostic semantics. We implemented an ontological Knowledge Base Server, which can expose the functionality of arbitrary off- the-shelf ontology management systems via a formally specified and well de- fined API. A case study was carried out in order to demonstrate the feasibility of our approach to use an ontological Knowledge Base Server as a registry for ubiquitous computing systems. 1 Introduction With the recent emergence of Semantic Web technologies like RDF(S) [1], DAML+OIL [2], and their common Description Logics (DL) [3] based successor OWL [4] numerous ontologies have been developed to conceptualize a plethora of domains of discourse [5]. This paper introduces an approach to model a ubiquitous computing domain of discourse with the Web Ontology Language OWL. This effort was carried out in course of the CHIL research project [6], which builds non-intrusive services aiming to introduce computers into the loop of humans. In order to imple- ment such services, a semantic middleware is being developed that fuses information provided by numerous perceptual components. Each perceptual component (e.g. image and speech recognizers, body trackers, etc.) contributes to the common domain