Measuring goal-oriented requirements language actor stability

Background: Goal models describe interests, preferences, intentions, desired goals and strategies of intervening stakeholders during the early requirements engineering stage. When capturing the requirements of real-world systems such as socio-technical systems, the produced goal models evolve quickly to become large and complex. Hence, gaining a sufficient level of understanding of such goal models, to perform maintenance tasks, becomes more challenging. Metric-based approaches have shown good potential in improving software designs and making them more understandable and easier to maintain. Aim: In this paper, we propose a novel metric to measure GRL (Goal-oriented Requirements Language) "actor stability" that provides a quantitative indicator of the actor maintainability. Method: We first, validate the proposed metric theoretically then empirically using a case study of a GRL model describing the fostering of the relationship between the university and its alumni. Results: The proposed actor stability metric is found to have significant negative correlation with the maintenance effort of GRL models. Conclusions: Our results show that the proposed metric is a good indicator of GRL actors' stability.