Quality of Service (QoS) becomes an important issue as systems are more open, therefore less predictable. In such contexts it is difficult to ensure via static approaches that a system will provide the expected QoS. In dynamic approaches, services are adapted to provide the best QoS according to the execution context. This article describes an object-based framework to deal with QoS in domains in which temporal faults is a major QoS criterion. The QoS optimization policy influences most of the architectural design decisions. The implementation is based on metaobjects that collectively manage the QoS and form a two decision-levels framework: at global level, objects share the same decision policy aiming to reduce timing faults, while at object level any specific QoS criteria may be applied. QoS description is made using UML extension mechanisms. Finally, the main phases of QoS management are detailed: prediction, establishment and operational, including observation and negotiation.'