Evaluating evolvability of computer based systems architectures-an ontological approach

System evolvability is a system's ability to withstand changes in its requirements, environment and implementation technologies. The need for greater systems evolvability is becoming recognised, especially in the engineering of computer based systems, where the development, commissioning and replacement of large systems is highly resource intensive. Despite this need, there are no formal means for evaluating the evolvability of a system and thus no means of proving that one system is more evolvable than another. Recognising this, we review the nature of change and evolution with respect to computer based systems. We contend that a systems architecture is the best level of abstraction at which to evaluate its evolvability. An ontological basis which allows for the formal definition of a system and its change at the architectural level is presented and applied to the domain of computer based systems engineering. Utilising this definition of change we draw on the deeper ontological theories in order to establish a model of systems architecture evolution. This model is then applied to a small CBS for concept validation.