We discuss and analyse cooperation strategies for rewriting queries in a mediator architecture. According to this approach, the mediated schema of each mediator is dynamically updated through the cooperation with information sources and other mediators, strongly influenced by the queries submitted by a consumer. This approach allows a mediator to face systems where information sources and consumer needs are dynamic. From the analysis of different cooperation strategies arises that it is more efficient and effective to directly cooperate with information sources when the sources are few. Otherwise, it is more efficient to cooperate with other mediators.