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Event-based communication is popular in many areas of computing,
ranging from programming user interfaces to publish & subscribe
services. Existing event management systems concentrate on the
delivery of event notifications to groups of clients, which are
physically connected to computer networks. In most cases they rely
on the concept of an "event producer" and lack a component
for observing events themselves, especially regarding complex events
whose observation is distributed. Also, existing event management
systems are often not well suited for mobile computing environments,
particularly with respect to the volatility of wireless connections.
The Nexus project at the University of Stuttgart is examining
concepts and methods for supporting location- and spatial-aware
applications for mobile users. The goal is to develop a global open
platform serving as a middleware for these applications. The Nexus
Event Service will be a central component of this platform. Its
tasks comprise the observation of events, including complex
distributed events, and the delivery of event notifications to
interested clients.
This thesis consists of two main parts. The first part discusses the
relevant concepts of event-based communication and mobility. The
terminology and the event model are consolidated and extended to
cover spatial events. We define an event as an observable change in
the state of the environment model. Spatial events are events that
are based on the absolute position of objects in space or the
relative position of objects to each other. An example for such an
event is a user entering a given area or building.
The second part presents a high-level architecture for the Nexus
Event Service. It identifies three logical components: the
Observation Service, the Notification Service and the Predicate
Management component, which manages the information pertaining to
events and clients. We then discuss important architectural issues,
including alternatives for the distribution of the Event Service and
the interaction of the Event Service with other Nexus services and
clients. Finally, we show how spatial events can be observed in the
Nexus context.
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