Towards a UML profile for QoS: a contribution in the reliability domain

Non-functional attributes of software/hardware systems are aspects of interest to embed in modeling notations. In the last few years, extensions of UML in this direction have been proposed, and some of them have been recently adopted as final specifications, such as the UML Profile for Schedulability, Performance, and Time. In this paper we intend to further contribute to the integration of UML with non-functional aspects, and we devise a lightweight extension of UML (i.e., stereotypes, tagged values and constraints) to represent issues related to the reliability modeling of component-based systems. To a certain extent we lay on other profiles to make easier the embedding of such issues and to work toward a unifying UML profile for Quality of Service and Fault Tolerance. Our extensions mostly concern the fault forecasting task, which enables the specification of models describing the failure rates of components and combines them to obtain a reliability factor for the whole system. Example diagrams from an elevator system help to show how the concepts introduced here can be used to design reliability-integrated UML models of component-based systems. In order to demonstrate the practical benefits of our approach we also show how to fit the proposed tagged values into a reliability model.