This research was supported by a Human Capital and Mobility Postdoctoral Fellowship. I wish to thank: Adel Bouhoula and Michael Rusinowitch for their invaluable assistance with SPIKE; Pierre Lescanne for inviting me to visit Nancy where most of this research was performed; David Basin, Alan Bundy, Miki Hermann, Andrew Ireland, and Michael Rusinowitch for their comments and questions; the reviewers for their comments and suggestions; the members of the Eureca and Protheo groups at INRIA; and the members of the DReaM group at Edinburgh and the MRG groups in Trento and Genova.