Systematic Refinement of Softgoals Using a Combination of KAOS Goal Models and Problem Diagrams

Softgoals are goals that do not have a clear-cut criterion for their satisfaction (in contrast to so-called hardgoals). They are considered to be satisfied when there is sufficient positive and little negative evidence for this claim. Thus, they are expected to be satisfied within acceptable limits rather than absolutely. Examples of such softgoals are quality attributes such as safety, security, and trustworthiness. In a previous paper, we showed how the systematic refinement of goals can be supported by combining KAOS goal models and problem diagrams that are created based on the Six-Variable Model. Therein, we mainly focussed on hardgoals. In this paper, we show how the systematic refinement of softgoals can be supported. We mainly focus on security as a softgoal and show how it can be refined in a systematic way. However, our method can be used in the same way to systematically decompose other softgoals as well. The benefit of our method is that it results not only in detailed security requirements but helps also in making expectations to be satisfied e.g. by sensors, actuators, other systems, and users explicit.