One of the most important properties of a good software engineering process and of the design of the software it produces is robustness to changing requirements. Scenario-based analysis is a popular method for improving the flexibility of software architectures. This paper demonstrates a search-based technique for automating scenario-based analysis in the software architecture deployment view. Specifically, a novel parallel simulated annealing search algorithm is applied to the real-time task allocation problem to find baseline solutions which require a minimal number of changes in order to meet the requirements of potential upgrade scenarios. Another simulated annealing-based search is used for finding a solution that is similar to an existing baseline when new requirements arise. Solutions generated using a variety of scenarios are judged by how well they respond to different system requirements changes. The evaluation is performed on a set of problems with a controlled set of different characteristics.

Previous research which has considered task allocation and fault-tolerance together has concentrated on constructing schedules which accommodate a fixed number of redundant tasks. Often, all faults are treated as being equally severe. There is little work which combines task allocation with architectural level fault-tolerance issues such as the number of replicas to use and how they should be configured, both of which are tackled by this work. An accepted method for assessing the impact of a combination of faults is to build a system utility model which can be used to assess how the system degrades when components fail. The key challenge addressed here is how to design objective functions based on a utility model which can be incorporated into a search algorithm in order to optimise fault-tolerance properties. Other issues such as how to extend the local search neighbourhood and balance objectives with schedulability constraints are also discussed.

Handling mode changes is one of the most complex and important problems for real-time systems designers. The challenge is to move a system from running one set of software to another while still achieving the quality of service guarantees necessary. There has been previous work which concentrated on how to perform scheduling and timing analysis of mode changes. However, a common theme of all this research is that if the system's schedule and allocation is chosen to minimise the set of differences between modes then the mode transition problem can be performed more easily and quickly. This paper investigates how this can be achieved