[SystemSafety] Software reliability (or whatever you would prefer to call it)

[Martyn Thomas]

Yes, it's astonishing how few people realise that you need a large
enough, representative enough sample before you can apply statistics.
Maybe it's the fault of our schools.

Martyn

On 06/03/2015 10:37, Nick Tudor wrote:
> Martyn
>
> Consider this then:
>
> The beta testing does not find any errors....according to your
> example, it must be 100% reliable.
>
> The fact that it did not hit the one undetected error in the code that
> would cause a system failure does not reflect in the supposed
> "reliability".
>
> Oh, then the software gets released and someone uses it in a manner
> such that it always hits the error - must be 0% reliable in the users
> view.  
>
> Which would you like to pick?
>
> Nick Tudor
> Tudor Associates Ltd
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> On 6 March 2015 at 09:55, Martyn Thomas
> <martyn at thomas-associates.co.uk
> <mailto:martyn at thomas-associates.co.uk>> wrote:
>
>     I'm puzzled by much of this discussion. Consider this common example:
>
>     A company creates a software package and submits it for beta
>     testing by
>     a group of users. Assume that the package reports how often it is used
>     and for how long, and the users report all errors they encounter.
>     Assume
>     there is a single instance of the software on a server that all the
>     users use.
>
>     The company corrects some of the errors that are reported.
>
>     The company calculates some measure of the amount of usage before
>     failure. Call it MTBF.
>
>     The MTBF is observed to increase.
>
>     What word shall we use to describe the property of the software
>     that is
>     increasing?
>
>     I'd call it "reliability". If you would, too, then how can software
>     reliability not exist?
>
>     I don't mind if you want to use a different word to describe the
>     property. Let's just agree one, do a global replace in the offending
>     standards and move on ...
>
>     ... to discussing a practical upper bound on the "reliability"
>     that can
>     be assessed in this way - and on the assumptions that should be made
>     explicit before using any such assessment as a prediction of future
>     performance.
>
>     Martyn
>
>
>
>
>
>
>
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