[SystemSafety] Relationship of reliability and safety (was Re: New paper on MISRA C)

[Paul Sherwood]

On 2018-09-13 08:35, Stefan Winter wrote:
> On 09/13/2018 07:57 AM, Paul Sherwood wrote:
>> On 2018-09-12 16:05, Peter Bernard Ladkin wrote:
>>> I suggest the following characterisation is somewhat misleading:
>>>> MIT and others have successfully debunked the notion that system 
>>>> safety is correlated with component reliability
>> 
>> OK, I'll try to be clearer. Engineering A Safer World states, with 
>> clear examples and justification:
>> 
>> "High reliability is neither necessary nor sufficient for safety."
> 
> could you please state where? The PDF search is highly unreliable for
> that document. ;)

It's stated after justification on Page 13, and re-stated along with 
several other old vs new assumptions on Page 48. I'm going to ask Nancy 
if the work can be converted into something text-searchable.

> To rebut a statement of such generality as "reliability is
> necessary/sufficient for safety" is easy if you read it as meaning
> "for all possible systems". One counterexample and you're done. I
> wonder, though, if such a statement is really meaningful, because the
> rebuttal also works in the opposite direction: "For any possible
> system reliability is never necessary for safety". I would assume that
> this is easier to disprove than to prove.

Fair enough. However while the theoretical and philosophical discussion 
is interesting, I'm ultimately trying to understand the practical 
engineering implications :-)

br
Paul