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Conservative Claims for the Probability of Perfection of a Software-based System Using Operational Experience of Previous Similar Systems

Zhao, X. ORCID: 0000-0002-3474-349X, Littlewood, B., Povyakalo, A. A. , Strigini, L. & Wright, D. (2018). Conservative Claims for the Probability of Perfection of a Software-based System Using Operational Experience of Previous Similar Systems. Reliability Engineering and System Safety, 175, pp. 265-282. doi: 10.1016/j.ress.2018.03.032


We begin by briefly discussing the reasons why claims of probability of non-perfection ( pnp ) may sometimes be useful in reasoning about the reliability of software-based systems for safety-critical applications. We identify two ways in which this approach may make the system assessment problem easier. The first concerns the need t o assess the chance of lifetime freedom from failure of a single system . The second concerns the need to assess the reliability of multi-channel software-diverse fault tolerant systems – in this paper, 1-out-of-2 systems. In earlier work (Littlewood and Rushby 2012, Littlewood and Povyakalo 2013) it was proposed that, in certain applications, claims for possible perfection of one of the channels in such a system may be feasible. It was shown that in such a case there is a particularly simple conservative expression for system pfd (probability of failure on demand) , involving the pfd of one channel , and the pnp of the other. In this paper we address the problem of how to assess such a pnp . In previous work (Zhao 2015) we have addressed this problem when the evidence available is only extensive failure - free working of the system in question. Here we consider the case in which there is, in addition , evidence of the previous success of the software development procedures used to build the system: specifically, several previous similar systems built using the same process have exhibited failure -free working during extensive operational exposure.

Publication Type: Article
Additional Information: © 2018 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license
Publisher Keywords: Fault-free software; probability of perfection; 1 -out- of-2 system reliability; software diversit y; operational experience; Bayesian modeling; limited prior belief; guaranteed-conservative reliability claims
Departments: School of Mathematics, Computer Science & Engineering > Computer Science > Software Reliability
Text - Accepted Version
Available under License Creative Commons Attribution Non-commercial No Derivatives.

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