Proven in Use for Software: Assigning an SIL Based on Statistics

Authored by: Jens Braband , Heinz Gall , Hendrik Schäbe

Handbook of RAMS in Railway Systems

Print publication date:  March  2018
Online publication date:  March  2018

Print ISBN: 9781138035126
eBook ISBN: 9781315269351
Adobe ISBN:


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The nature of software failures and the possibility to predict software failure behavior has attracted the interest of researchers and engineers. The first have tried to study the phenomenon, and the second have been searching for a way to predict software failure behavior based on characteristics describing the software, preferably characteristics of the source code as metrics. In order to approach this problem, first of all, one needs to understand the nature of software failure behavior. Obviously, this is different from hardware failure behavior. One main question is whether software failure behavior can be described by probabilistic models. If such a model is known, the next question is then how it can be used and whether it would be possible to use this model for prediction or to prove that a certain piece of software falls, e.g., into a safety integrity level regarding its failure rate (if this exists) and can therefore be judged to be qualified for this safety integrity level. Proven-in-use arguments are needed when predeveloped products with an in-service history are to be used in different environments than those they were originally developed for. Particular cases may include the following:

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