[SystemSafety] What do we know about software reliability?

[Peter Bernard Ladkin]

On 2020-09-15 14:57 , Derek M Jones wrote:
>  
> The ANSI definition is encompasses what needs to be said:
> "Software Reliability is defined as: the probability of failure-free software operation for a
> specified period of time in a specified environment."
> 
> The "specified environment" is what tends to get ignored in most analysis.
I agree.

There is but one definition of "software reliability" which comes up in the IEC Glossary, and it is
in the control-systems-for-NPPs part:

"EN	software reliability
component of the system reliability related to software failures"

There are forty definitions of "reliability" in the IEC glossary. Most of them speak of kit

* performing a required function/expected function
* for a given/specified period of time/time interval
* under given/stated conditions/operating conditions

That is all consistent with the definition given by Derek.

The main difference among the more-similar definitions is whether it is said to be an "ability" of
the kit, or a "probability". The "ability" generally indicates "exceptionlessly". So the difference
is between an absolute notion and one which admits partial/likely fulfilment of the property.

I have no idea why anyone might complain generally about such definitions. They are ubiquitous in
electrical engineering and make plain sense (although one can quibble about the precise phrasing -
and does!).

PBL

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





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