Reasoning About Confidence and Uncertainty in Assurance Cases: A Survey

Assurance cases are structured logical arguments supported by evidence that explain how systems, possibly software systems, satisfy desirable properties for safety, security or reliability. The confidence in both the logical reasoning and the underlying evidence is a factor that must be considered carefully when evaluating an assurance case; the developers must have confidence in their case before the system is delivered and the assurance case reviewer, such as a regulatory body, must have adequate confidence in the case before approving the system for use. A necessary aspect of gaining confidence in the assurance case is dealing with uncertainty, which may have several sources. Uncertainty, often impossible to eliminate, nevertheless undermines confidence and must therefore be sufficiently bounded. It can be broadly classified into two types, aleatory (statistical) and epistemic (systematic). This paper surveys how researchers have reasoned about uncertainty in assurance cases. We analyze existing literature to identify the type of uncertainty addressed and distinguish between qualitative and quantitative approaches for dealing with uncertainty.