Towards contractual interfaces for reusable functional quality attribute operationalisations

The quality of a software system can be measured by the extent to which it possesses a desired combination of quality attributes (QAs). While some QAs are achieved implicitly through the interaction of various functional components of the system, others (e.g., security) can be encapsulated in dedicated software components. These QAs are known as functional quality attributes (FQAs). As applications may require different FQAs, and each FQA can be composed of many concerns (e.g., access control and authentication), integrating FQAs is very complex and requires dedicated expertise. Software architects are required to manually define FQA components, identify appropriate points in their architecture where to weave them, and verify that the composition of these FQA components with the other components is correct. This is a complex and error prone process. In our previous work we defined reusable FQAs by encapsulating them as aspectual architecture models that can be woven into a base architecture. So far, the joinpoints for weaving had to be identified manually. This made it difficult for software architects to verify that they have woven all the necessary FQAs into all the right places. In this paper, we address this problem by introducing a notion of contract for FQAs so that the correct application of an FQA (or one of its concerns) can be checked or, alternatively, appropriate binding points can be identified and proposed to the software architect automatically.