[SystemSafety] [System Safety] FOSDEM talk by Paul Sherwood

[Prof. Dr. Peter Bernard Ladkin]

Derek,

On 2025-02-11 13:34 , Derek M Jones wrote:
> Peter,
>
>>> That is exactly what we are working on. First off we've had to categorically establish that 
>>> software in these new systems exhibits random behaviour, and then show that we could apply 
>>> statistical techniques to model failure rates with confidence intervals. 
>>
>> Littlewood and Strigini showed clearly in 1993 that you can't use statistical evaluation to 
>> establish positively the safety requirements of safety functions with SIL2 - SIL4 reliability 
>> requirement. (You can use statistical evaluation in hindsight to assess whether your system did 
>> achieve was it was intended to achieve, but you usually need years - or decades - of operational 
>> experience.)
>
> I assume you mean the paper
> "Validation of Ultrahigh Dependability for Software-Based Systems"
> https://openaccess.city.ac.uk/id/eprint/1251/1/CACMnov93.pdf
>
> What they actually say is that it requires a lot of work, implying that
> it may be too expensive or time consuming to be be cost effective

There is often a difference between what people choose to write in a paper, and what the important 
result is.

I said what the result is, above. Having worked with Bev and others for some 16+ years now on this 
very issue, I ask you (and others) to take it from me on what it says, and the 50 words above 
summarise it.

PBL

Prof. Dr. Peter Bernard Ladkin
Causalis Limited/Causalis IngenieurGmbH, Bielefeld, Germany
Tel: +49 (0)521 3 29 31 00