[SystemSafety] What do we know about software reliability?

[Derek M Jones]

Hugues
> if A then
>    do_nothing
> else
>    fail --potentially hurt and kill people
> end if
> 
> end
> 
> The specification of the software is to do nothing;
> NB: I'm not asking if it is the best implementation, whatever the criteria are, but just : "is it reliable?"

The "if A then"
could be unreliable, in that a cosmic ray could flip its value.

There are research compilers that reduce the likelihood of a
cosmic ray altering the behavior of a program:
http://shape-of-code.coding-guidelines.com/2011/11/07/compiling-to-reduce-the-impact-of-soft-errors-on-program-output/

Circa 2011, 1-bit of a 4GB RAM had its value flipped roughly every 33
hours as a result of a cosmic ray hitting the upper atmosphere.

> regards,
> 
> Hugues
> 
> 
> ----- Mail original -----
>> De: "Peter Bernard Ladkin" <ladkin at causalis.com>
>> À: systemsafety at lists.techfak.uni-bielefeld.de
>> Envoyé: Mardi 15 Septembre 2020 19:58:45
>> Objet: Re: [SystemSafety] What do we know about software reliability?
>>
>> Bev and I and Dewi have a colleague who poses the following question.
>>
>> "We have clients who have installed hundreds of [examples of our kit]
>> over the last ten years, and
>> have never seen any failure. They want to use it in further systems
>> that they build. What arguments
>> do we/they need to provide in order validly to justify such further
>> use?"
>>
>> So, what is the answer to that question?
>>
>> PBL
>>
>> Prof. Peter Bernard Ladkin, Bielefeld, Germany
>> Styelfy Bleibgsnd
>> Tel+msg +49 (0)521 880 7319  www.rvs-bi.de
>>
>>
>>
>>
>>
>>
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-- 
Derek M. Jones           Evidence-based software engineering
tel: +44 (0)1252 520667  blog:shape-of-code.coding-guidelines.com