Re: [SystemSafety] Fault, Failure and Reliability Again (short)

From: Peter Bernard Ladkin < >
Date: Wed, 04 Mar 2015 14:38:46 +0100


Michael,

On 2015-03-04 13:54 , C. Michael Holloway wrote:
> On 3/4/15 7:14 AM, Peter Bernard Ladkin wrote:

>> Although I do find reconciling concepts a less odd activity than responding to suggestions that
>> the field in which some of the scientists I most respect have worked for four decades actually
>> doesn't exist!

> I don't think anyone has claimed that the field doesn't exist.

Have you been dreaming or have I? At least two people here have claimed that software can't have failures, and so any notion of assessing a rate of railure per demand or per time unit is meaningless.

That is saying that the field, of studying the rate of failure of software per demand or per time unit, does not exist.

> Some have claimed that the work
> conducted in the field has not yet borne any healthy fruit. Some, myself included, doubt it ever will.
>
> No one should be surprised if those claims and doubts turn out to be accurate. Even a casual look
> at the history of science will show that it is not all that uncommon for respected scientists to
> work for decades in areas that turn out to be (at best) fruitless.

Both the civil large-aeroplace certification standards and IEC 61508 specify criteria for the reliability of kit, which includes elements whose behavior is largely driven by software, in terms of dangerous failure rates, either per demand or per time unit. That inevitably (as I have argued) puts similar such demands on the software itself.

If certification requirements, respectively safety standards, require such measures to be demonstrated, then people will be studying them in terms of engineering science and obtaining what helpful results they can obtain.

If that's all futile because the "area.... turn[s] out to be fruitless" then those standards had better be rewritten pronto, because they obviously can't be fit for purpose if they demand properties of kit that cannot be shown and have no hope of being shown.

PBL Prof. Peter Bernard Ladkin, Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany Je suis Charlie
Tel+msg +49 (0)521 880 7319 www.rvs.uni-bielefeld.de



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