Using UML to specify QoS constraints in ODP
This paper is concerned with Quality of Service (QoS) specification in distributed system design. The specification and implementation of QoS is increasingly important in distributed systems due to the need to address questions of performance, particularly for systems involving multimedia. To ensure correct implementation of QoS requirements, statements of QoS need to be introduced early in the design process, and in terms of design we consider the use of the Unified Modelling Language (UML), which has quickly become the de facto standard for object-based designs.The framework we use for distributed system construction is that provided by the open distributed processing reference model, and we focus in particular on its computational viewpoint. The aim of this paper is to construct a UML model of the computational viewpoint focusing on the description of QoS within that viewpoint. To specify the QoS aspects of computational objects in the UML model, we use a real-time logic called QL. In order to express further constraints on the UML model of the computational viewpoint, we use the Object Constraint Language to express invariants that each instance of our model must satisfy. The purpose of our UML model of the computational viewpoint is to act as a template via which specific distributed system designs can be constructed and we illustrate this with the specification of a lip synchronisation mechanism.