QoS-based flexibility in distributed systems

This paper discusses how to make a distributed object system flexible so as to satisfy the application's requirement in the change of the system environment. Each object supports other objects with quality of service (QoS). The change of the system is modeled to be the change of QoS supported by the objects. We discuss relations among the operations with respect to QoS, i.e. QoS-based equivalency and compatibility of the operations. By using the QoS-based relations, we newly discuss a QoS-based compensating way to recover from the less qualified state. Finally, we discuss QoS-based replicas of objects.