Such mediating services must be of value to the customers, so that it will benefit their client applications to access mediators rather than the server sources directly. Applications that benefit from mediation include planning and other decision-making tasks that require information from diverse resources, as databases, reference systems, data obtained from sensors, and analyses for projecting trends into the future. The sources are often autonomous, some of them are public, and will typically be heterogenous. The heterogeneities include representation, scope, level of abstraction, and context. Mediated results are intented to be composable by higher level application programs, so that the applications can solve problems involving multiple subtasks and multiple domains.
Mediation requires domain expertise, and mediators are hence domain-specific.
Mediators need a machine-friendly interface to support their client applications. This interface must provide good communication, while encapsulating the mediation tasks, so that the complexity of the composed system is not much greater than that of the individual subtasks. However, questions of effectiveness and efficiency do arise, and must be dealt with by exploiting the processing and storage capabilities of modern hardware. The corresponding architecture is best viewed as a generalization of a server-client model. The concept is network-oriented, and mediating services are best provided over the network by domain specialists.