[SystemSafety] Paper on Software Reliability and the Urn Model

[Derek M Jones]

All,

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