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

From: Nick Tudor < >
Date: Fri, 6 Mar 2015 10:37:13 +0000


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_xxxxxx 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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