There are a number of people without whom this thesis would not have been feasible. Their high academic standards and personal integrity provided me with continuous guidance and support.

Firstly, I would like to thank my doctoral advisor Professor Günther for his continuing support, motivation and valuable input throughout the entire time of this doctoral thesis.

I would like to thank my co-advisor Professor Kobsa for his comprehensive academic guidance and for hosting me at the University of California, Irvine.

My appreciation goes to Professor Berendt who gave me advice, encouragement and valuable feedback innumerable times.

I would like to thank my colleagues from the Berlin-Brandenburg Graduate School in Distributed Information Systems for their inspiring discussions and feedback. I thank the Deutsche Forschungsgemeinschaft for the funding of my scholarship (DFG grant no. GRK 316/3) and the Alexander v. Humboldt Foundation (TransCoop Program) and the National Science Foundation (Grant No. 0308277) for their financial support.

I thank Sören Preibusch for his reliable assistance during this thesis. Thanks also go to my office mates Anett Kralisch and Claus Boyens for their great company.

This thesis is dedicated to my parents, Karin and Peter Teltzrow, without whom none of this would have been possible.