We prove that all rewriting queries are found and we characterize the complexity. Mediators, such as MIX, have to provide DTDs of the views that they compute in order to facilitate query formulation, query processing, and so on. However, a view has more than one DTDs. Discusses the similarities and differences between metasearchers, asknown in the IR community, and mediators, as known in the database community. In AAAI98 Workshop on AI and Data Integration .
Mediators create virtual entities from information that is distributed across multiple sources.
Fusion queries select the entities that satisfy some user-specified conditions. The fusion query optimization problem becomes particularly challenging when the conditions have to be tested on multiple sources. We show that under common assumptions a limitedclass of plans, the semijoin adaptive plans, contain the optimal fusionplan. An experimental evaluation delivers further results on choosingthe optimal fusion plan. In Journal of Logic Programming .