Expert Assessment of Arguments: A Method and Its Experimental Evaluation
SAFECOMP '08 Proceedings of the 27th international conference on Computer Safety, Reliability, and Security
A new approach to assessment of confidence in assurance cases
SAFECOMP'12 Proceedings of the 2012 international conference on Computer Safety, Reliability, and Security
A systematic approach to justifying sufficient confidence in software safety arguments
SAFECOMP'12 Proceedings of the 31st international conference on Computer Safety, Reliability, and Security
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Society is increasingly requiring quantitative assessment of risk and associated dependability cases. Informally, a dependability case comprises some reasoning, based on assumptions and evidence, that supports a dependability claim at a particular level of confidence. In this paper we argue that a quantitative assessment of claim confidence is necessary for proper assessment of risk. We discuss the way in which confidence depends upon uncertainty about the underpinnings of the dependability case (truth of assumptions, correctness of reasoning, strength of evidence), and propose that probability is the appropriate measure of uncertainty. We discuss some of the obstacles to quantitative assessment of confidence (issues of composability of subsystem claims; of the multi-dimensional, multi-attribute nature of dependability claims; of the difficult role played by dependence between different kinds of evidence, assumptions, etc). We show that, even in simple cases, the confidence in a claim arising from a dependability case can be surprisingly low.