Littlewood, B. and Povyakalo, A. A. (2012).
Conservative reasoning about epistemic uncertainty for the probability of failure on demand of a 1outof2 softwarebased system in which one channel is "possibly perfect" (CSR Technical Report 20 March 2012).
London: Centre for Software Reliability, City University London.
Abstract
In earlier work, (Littlewood and Rushby 2011) (henceforth LR), an analysis was presented of a 1outof2 system in which one channel was “possibly perfect”. It was shown that, at the aleatory level, the system pfd could be bounded above by the product of the pfd of channel A and the pnp (probability of nonperfection)of channel B. This was presented as a way of avoiding the wellknown difficulty that for two certainlyfallible channels, system pfd cannot be expressed simply as a function of the channel pfds, and in particular not as a product of these. One price paid in this new approach is that the result is conservative – perhaps greatly so. Furthermore, a complete analysis requires that account be taken of epistemic uncertainty – here concerning the numeric values of the two parameters pfdA and pnpB. This introduces some difficulties, particularly concerning the estimation of dependence between an assessor’s beliefs about the parameters. The work reported here avoids these difficulties by obtaining results that require only an assessor’s marginal beliefs about the individual channels, i.e. they do not require knowledge of the dependence between these beliefs
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Conservative reasoning about epistemic uncertainty for the probability of failure on demand of a 1outof2 softwarebased system in which one channel is "possibly perfect". (deposited 25 Sep 2012 14:17)
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