In this paper we investigate the observation of physical world events, i.e. events that occur in the physical world, and are observed through model data, part of which is collected by sensors. The physical world events of interest here are those that are suitable for proactively supporting mobile users. This means that they have to be on the same highabstraction level as perceived by the user. In a large-scale system as we envision it, the model data needed for the observation of these high-level physical world events may be distributed over multiple servers.

We first present a requirement analysis. Then we propose an event service architecture that fulfills the requirements. Finally, we show the scalability of the approach through an evaluation based on a prototype implementation.