Using quality of service bounds for effective multi-objective software architecture optimization

Quantitative prediction of non-functional properties, such as performance, reliability, and cost, of software architectures supports systematic software engineering. Even though there usually is a rough idea on bounds for quality of service, the exact required values may be unclear and subject to tradeoffs. Designing architectures that exhibit such good tradeoff between multiple quality attributes is hard. Even with a given functional design, many degrees of freedom in the software architecture (e.g. component deployment or server configuration) span a large design space. Automated approaches search the design space with multi-objective meta-heuristics such as evolutionary algorithms. However, as quality prediction for a single architecture is computationally expensive, these approaches are time consuming. In this work, we enhance an automated improvement approach to take into account bounds for quality of service in order to focus the search on interesting regions of the objective space, while still allowing trade-offs after the search. To validate our approach, we applied it to an architecture model of a component-based business information system. We compared the search to an unbounded search by running the optimization 8 times, each investigating around 800 candidates. The approach decreases the time needed to find good solutions in the interesting regions of the objective space by more than 35% on average.