ARRL: A Criterion for Composable Safety and Systems Engineering

While safety engineering standards define rigorous and controllable processes for system development, safety standards’ differences in distinct domains are non-negligible. This paper focuses in particular on the aviation, automotive, and railway standards, all related to the transportation market. Many are the reasons for the said differences, ranging from historical reasons, heuristic and established practices, and legal frameworks, but also from the psychological perception of the safety risks. In particular we argue that the Safety Integrity Levels are not sufficient to be used as a top level requirement for developing a safety-critical system. We argue that Quality of Service is a more generic criterion that takes the trustworthiness as perceived by users better into account. In addition, safety engineering standards provide very little guidance on how to compose safe systems from components, while this is the established engineering practice. In this paper we develop a novel concept called Assured Reliability and Resilience Level as a criterion that takes the industrial practice into account and show how it complements the Safety Integrity Level concept.