[SystemSafety] Paper on Software Reliability and the Urn Model

Derek M Jones derek at knosof.co.uk
Wed Feb 25 12:27:50 CET 2015


On 25/02/2015 10:37, jean-louis Boulanger wrote:
> 2015-02-25 10:00 GMT+01:00 Peter Bernard Ladkin <ladkin at rvs.uni-bielefeld.de
>> I have recently been involved in discussions concerning rewriting IEC
>> 61508-7:2010 Annex D, a short
>> informative section attempting to explain the statistical evaluation of
>> the reliability of SW for
>> which there is an operational history.

Calculating reliability is in the details.  Are there enough details
in the operational history?

> For the software, no evaluation of reliability are acceptable or
> representative.

It is more accurate to say the cost of providing an evaluation
of software reliability that is sufficiently accurate is greater
than people are willing to pay.

>> Some professionals don't even like the urn model for explaining SW
>> reliability (you know who you
>> are! :-) ). But I think it's pretty good for some purposes, even though in

A model that does not reflect reality is one good reason for not liking
the urn model.

But the urn model does has a level of brand name recognition that
none of the other models have.

Nature abhors a vacuum and the urn model is an easy sell.  Nobody has
good enough data that an alternative model would need to overcome
the brand name advantage of the urn model.

Derek M. Jones           Software analysis
tel: +44 (0)1252 520667  blog:shape-of-code.coding-guidelines.com

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