These resources are typically developed and maintained autonomously of most of the applications that use their results. Decision support applications are typically designed subsequently and independently. Planning support is synchronized with management objectives, and has to rely on existing sources, since it is rare that sufficient time is available to build planning systems and their data collection from scratch. Other sources of information are systems as digital libraries, geographic information systems, and simulations. Dealing with many, diverse, and heterogeneous sources overwhelms high-level applications with excessive emphasis on irrelevant, but crucial details.
Mediators provide intermediary services, linking data resources and application programs.
Their function is to provide integrated information, without the need to integrate the data resources. Specifically, the tasks required to carry out these functions are comprised of 1. Accessing and retrieving relevant data from multiple heterogeneous resources 2. Abstracting and transforming retrieved data so that they can be integrated 3. Integrating the homogenized data according to matching key data 4.