Commercially available middleware systems today offer best-effort Quality-of-Service (QoS) to the application programs. Due to the natural limitation of resources and the differences between the priorities and demands of applications, middleware systems must have the capability to offer varying degrees of QoS. The QoS requirements of middleware applications can be monitored and fulfilled by configuring the middleware. This could be implemented, for example, by encapsulating the specific QoS concerns of middleware within the components and by installing the most suitable component on a particular QoS demand. Unfortunately, not all the QoS concerns of a distributed system can be defined and encapsulated by the interfaces of components. So-called crosscutting aspects hinder the adaptation of middleware systems since the implementations of QoS support techniques cannot be restricted to the implementations of components. We propose a reflective and aspect-oriented technique based on the principle of Composition-Filters to address this problem
