Representation of Confidence in Assurance Cases Using the Beta Distribution

Abstract

Assurance cases are used to document an argument that a system -- such as a critical software system -- satisfies some desirable property (e.g., safety, security, or reliability). Demonstrating high confidence that the claims made based on an assurance case can be trusted is crucial to the success of the case. Researchers have proposed quantification of confidence as a Baconian probability ratio of eliminated concerns about the assurance case to the total number of identified concerns. In this paper, we extend their work by mapping this discrete ratio to a continuous probability distribution -- a beta distribution -- enabling different visualizations of the confidence in a claim. Further, the beta distribution allows us to quantify and visualize theuncertainty associated with the expressed confidence. Additionally, by transforming the assurance case into a reasoning structure, we show how confidence calculations can be performed using beta distributions.