Adaptive selection of materialized queries in a mediator

In a mediator, query usage should be carefully monitored to determine the optimized set of materialized sub-queries, since the integration schema of a mediator can be incrementally modified and the evaluation frequency of a global query can also be continuously varied. This paper proposes a theoretical basis for adaptive selection of materialized sub-queries such that available storage in a mediator can be highly utilized at any time. In order to differentiate the recent usage of a query from the past, the accumulated usage frequency of a query decays as time goes by. Consequently, it is possible to find the optimum set of materialized sub-queries which minimizes the total evaluation cost of global queries in linear search complexity.