A Complexity Measure for System Safety Assurance

Abstract

This paper describes a two‐year research effort to define complexity measures for avionics systems in order to help the FAA identify when systems are too complex to be able to assure their safety. The research project developed a measure of complexity related to the number of ways that an avionics system error (fault) could propagate from one element to another. Since each potential propagation requires another sub‐argument in the safety case, the number of such arguments should be proportional to certification effort. Thus, the ability to show that the system is safe, through the certification process, should depend on whether a system has low enough complexity (number of ways for errors to propagate). Our results include a formula for estimating the “error‐propagation complexity” from a system design, the results of using that formula on small and medium systems, and steps for using the formula. The test of the formula was performed by repeating that calculation on a second design for the first system and briefly on a larger design identified by the FAA, from a NASA technical report.

(Draft) Engineering Trustworthy Secure Systems

“…Complexity also increases the costs and difficulty of performing systems analyses for loss. That is, systems may be too complex to be analyzed for adequate assurance [Sheard18].…”

Engineering Trustworthy Secure Systems

“…Consequently, many principles deal with reducing and managing complexity and creating systems that can be more easily evaluated. See [Sheard18] for discussions on how systems may be too complex to be analyzed for adequate assurance. 76 The term information hiding, also called representation-independent programming, is a design discipline to ensure that the internal representation of information in one system component is not visible to another system component invoking or calling the first component, such that the published abstraction is not influenced by how the data may be managed internally.…”