[SystemSafety] What do we know about software reliability?

[Nick Tudor]

Spot on Hugues.  It could have been asked that if a comet hit the thing
that had contained the hardware that ran the software (....that flipped a
bit or two (!)....) does that make the software 'unreliable' then....?
Doh!  Too many times the argument over the 'reliability' of software comes
down to the reliability of hardware or the inability of humans to
understand the environment in which they put the software and defend
against foreseeable issues (like bit flips).

Nick Tudor
Tudor Associates Ltd
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On Wed, 16 Sep 2020 at 07:10, Hugues Bonnin <hugues.bonnin at free.fr> wrote:

> Derek,
>
> You do not mention cause of software unreliability, but of the hardware
> which executes it.
> My question is on software reliability.
>
> Regards
>
> Hugues
>
>
>
> > Le 16 sept. 2020 à 03:05, Derek M Jones <derek at knosof.co.uk> a écrit :
> >
> > 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
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