Section: Application Domains
In the absence of sufficient or sufficiently accurate knowledge, adaptive methods have been developed for query execution, that allow to alternate query processing with query execution phases. This was introduced long ago in system R  for situations where the statistics would be misleading or incomplete. This is now a topic of increasing interest with the development of applications running over data distributed over networks. Adaptation is the key challenge for ubiquitous networks. More generally, the capacity to self-assemble, grow, repair, organize, evolve over long period of time while maintaining essential functionalities is of fundamental importance for networks of cooperating objects. The combination of networking and application layers, jointly processed by distributed query engines, offers a huge potential for pervasive adaptation, because the query engine can adapt the queries to the network (adaptive evaluation) and the network to the queries (Quality of service and content based routing).