Value-added Mediation in Large-Scale Information Systems [chapter]

Gio Wiederhold
1997 IFIP Advances in Information and Communication Technology  
Many information-processing tasks can be part of multiple customer applications, as summarizing stock prices, integrating catolog information from several companies in the same line of business, predicting the weather, and checking on transportation resources. We assign such sharable services to an active rniddleware layer, interposed between clients and servers. We define domain-specific mediator modules to populate this layer. Such mediating services must be of value to the customers, so that
more » ... it will benefit their client applications to access mediators rather than the server sources directly. Several categories of value can be considered: improvement in access and coverage, improvement of content, and delegation of maintenance. We will define criteria for mediating modules: ownership by party who assumes responsibility for the rseults of the services, domain-specificity to delimit the scope of such a responsibility, and, of course, conformance with interface standards that enable interoperation. Applications that benefit from mediation include planning and other decisionmaking 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 domainspecific. 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 R. Meersman et al. (eds.), Database Applications Semantics © IFIP International Federation for Information Processing 1997 Value-added mediation in large-scale information systems 35 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 partitioning into layers and by domain enhances maintainability: the applications software staff can concentrate on functional improvements, the data resource managers on operational issues, and the technical maintenance is concentrated in the mediator layer. The concept is network-oriented, and mediating services are best provided over the network by domain specialists. With suitable payment mechanisms, mediating services can be performed by independent entrepreneurs.
doi:10.1007/978-0-387-34913-8_3 fatcat:dv5pku7haraw3i43dman6l4roy