Re: [SystemSafety] Does "reliable" mean "safe" and or "secure" or neither?

From: Roberto Bagnara < >
Date: Sun, 24 Apr 2016 20:11:29 +0200

On 24/04/2016 18:36, Michael J. Pont wrote:
> Roberto asks:
> "Can we talk about the reliability of the components in the context
> of the overall system, without any knowledge about how they implement
> their functionality (e.g., hardware only, hardware + little bit of
> software, hardware + lots of software, hardware + software + humans)?"
> If our definition of reliability is something like this (from my previous
> email):
> "the extent to which an experiment, test, or measuring procedure yields the
> same results on repeated trials"

OK. In my example a "trial" would consist in exercising the overall system under in-spec conditions. The "experiment" would consist in recording the in-spec and out-of-spec behaviors of the various system components. We would say that two outcomes are "the same result" if they are either both in-spec or both out-of-spec. We perform many "repeated trials" and we thus determine the "reliability" of each component in the context of the overall system.

Do you think there is something flawed in the above? That is, do you think that the use of the word "reliability" in that context makes sense? If it does not make sense, can you please indicate where the flaw is? Kind regards,


P.S. Please try to resist the temptation to anticipate the fact

     that one day we will open the black boxes containing the components
     and perhaps we will find software in some of them.

     Prof. Roberto Bagnara

Applied Formal Methods Laboratory - University of Parma, Italy mailto:bagnara_at_xxxxxx

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systemsafety_at_xxxxxx Received on Sun Apr 24 2016 - 20:12:39 CEST

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