Introduction

Abstract

Location-based services (LBSs), i. e., services that adapt their behavior to the user’s location, have become a part of many people’s everyday lives. Applications, such as car, bicycle, and pedestrian navigation systems, GPS-based city tour guides, and friendfinder services, are getting more and more popular, and “impact individuals, organizations, and our society as a whole” (Raubal, 2011). Still most, if not all, current LBS products stay far beyond the general idea of context-aware services envisioned by the ubiquitous computing research community in the 1990’s. Dey and Abowd (1999), for instance, introduce primary context as those types of context “that are, in practice, more important than others. These are location, identity, activity and time” (p. 4). Secondary are all other types of context, and “they can be indexed by primary context because they are attributes of the entity with primary context.” (pp. 4-5). For finding out the weather forecast, for instance, the system needs the primary context information on location and time.