Quality-Driven Self-Adaptation: Bridging the Gap between Requirements and Runtime Architecture by Design Decision

Running with static requirements and design decisions, a software system cannot always perform optimally in a highly uncertain and rapidly changing environment. Quality-driven self-adaptation, which enables a software system to continually adapt its structure and behavior to improve the overall quality satisfaction, thus becomes a promising capability of software systems. Existing researches on self-adaptive systems, although having proposed effective methods and techniques on requirements-driven self-adaptation and reflective components, do not well address the gap between requirements and runtime architecture. In this paper, we propose a quality-driven self-adaptation approach, which incorporates both requirements- and architecture-level adaptations. At the requirements level, value-based quality tradeoff decisions are made with the aim of maximizing system-level value propositions. At the architecture level, component-based architecture adaptations are conducted. To bridge the gap between requirements and runtime architecture, design decisions capturing alternative design options and their rationales are introduced to help map requirements adaptations and context changes to adaptation operations on the runtime architecture. To validate the effectiveness, we implement the approach based on a reflective component model and conduct an experimental study on it. The results show that the approach leads to better performance compared with traditional software and the overall quality satisfaction is kept maintained. Furthermore, the development effort is affordable but the approach still has shortage in extensibility.