A subjective logic-based approach for assessing confidence in assurance case

Abstract

Assurance case has been widely used to justify safety, security and other properties of systems. The extent we can trust the assurance case, i.e., confidence in assurance case, is still an open issue in the area. This paper proposes a subjective logic based approach to assess the confidence in assurance case. Compare to other quantitative tools such as Bayesian Belief Network or Dempster-Shafer theory, subjective logic can (1) handle uncertainty and vagueness that usually are contained in expert opinions, and (2) provide appropriate logic operators to deal with different argument types. In the paper, we firstly define the concepts of confidence, sufficiency and necessity to measure the affecting factors to the confidence. Then, we identify four basic argument types and define confidence propagation rules for them. The confidence in assurance case can be calculated iteratively from the bottom up. The application of the proposed approach is illustrated by an industry case study.