[SystemSafety] What do we know about software reliability?

[Peter Bernard Ladkin]

On 2020-09-15 11:21 , Coq, Thierry wrote:
> ...Ariane A501 flight has disproved any probabilistic approach on software that would not
> start with a frequency of failure of 1. 

I have no idea what this sentence means.

I think everybody would agree that the environmental circumstances leading to failure of the Ariane
FLight 501 control system were certain to arise during launch. I don't see what probability has to
do with it.

Whatever people's inclinations to statistical evaluations of SW, we are about to be deluged by it.
The DLNN assistance functions in the automation of road vehicles can at present only be justified by
an assessment of their in-service behaviour. There are going to be numerical requirements on their
dependability and vendors will be providing argument that those numerical requirements are fulfilled.

The statisticians know well how much evidence has to be produced in order to derive conclusions on
reliability to an appropriate level of confidence. (See, for example, Peter Bishop's comment here on
the Tempe accident.) It is a lot higher than what, as far as I can tell, the vendors of such
equipment are likely be able to produce. What's going to happen?

PBL

Prof. Peter Bernard Ladkin, Bielefeld, Germany
Styelfy Bleibgsnd
Tel+msg +49 (0)521 880 7319  www.rvs-bi.de





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