Certus: A domain specific language for confidence assessment in assurance cases

TL;DR

The paper addresses the challenges of quantitative confidence assessment in assurance cases by introducing Certus, a DSL that models confidence with convex fuzzy sets on $eta=[0,1]$ and propagates confidence through argument DAGs using case based operators. It provides mechanisms for confidence assignment to leaves, various propagation semantics, and supports defeaters through pre flight checks, all aimed at improving interpretability and trustworthiness. Key contributions include formalizing confidence with fuzzy sets, enabling reusable propagation operators including macros such as FUSE, and demonstrating applicability with an automotive ACC fragment. The work lays a foundation for more transparent, scalable, and reusable confidence reasoning in ACs, with future work targeting formal specifications, graphical representations, and practitioner evaluations for real world impact.

Abstract

Assurance cases (ACs) are prepared to argue that a system has satisfied critical quality attributes. Many methods exist to assess confidence in ACs, including quantitative methods that represent confidence numerically. While quantitative methods are attractive in principle, existing methods suffer from issues related to interpretation, subjectivity, scalability, dialectic reasoning, and trustworthiness, which have limited their adoption. This paper introduces Certus, a domain specific language for quantitative confidence assessment. In Certus, users describe their confidence with fuzzy sets, which allow them to represent their judgment using vague, but linguistically meaningful terminology. Certus includes syntax to specify confidence propagation using expressions that can be easily inspected by users. To demonstrate the concept of the language, Certus is applied to a worked example from the automotive domain.

Figures (6)

• Figure 1: Visualization of a fuzzy set for "'high" confidence and plot of the corresponding fuzzy membership function.
• Figure 2: Some canonical sets defined by the Certus language.
• Figure 3: Simple propagation step in Certus.
• Figure 4: Using parameterized propagation operators.
• Figure 5: Example showing the expansion of the macro.