Maintaining maintainability

Conventionally, maintainability is seen as an attribute of software; measures which aim to quantify maintainability are all expressed in terms of attributes of the source code or related documentation. Such metrics do not correspond with intuition, and fail in important ways; for example they are not used by industry in assessing lifecycle costs. Maintainability is related to the skills of the maintenance team, the tools available, the maturity of the process and so on. We propose a new model, which takes a systemic view of the maintenance process and organisation as well as the software. The changing relationships between components of the model are identified as key properties for assessing maintainability. We suggest empirical approaches which could use the model to quantify maintainability. We hope the model could be used for assessing the effect of evolution, not only in the software, but in its environment.