Re: [SystemSafety] Degraded software performance [diverged from Fault, Failure and Reliability Again]

From: Michael J. Pont < >
Date: Thu, 5 Mar 2015 12:29:06 -0000

Dear Bertrand,

My views.

This is an important part of an important (and influential) document.

I believe that there are many people on this list who take the view that concept of "software reliability" (as used in this appendix) is flawed and unhelpful. Replacing this with another appendix that is based on the same concept does not seem to me to be a huge step forward.

There are other options.

Personally, I think that the appendix needs to be replaced with material that explains how pre-developed software should be qualified. The solution - I suggest - is that such software needs to have been developed according to the techniques detailed elsewhere in the standard (which is essentially what is required in a DO-178x project).


-----Original Message-----
From: systemsafety-bounces_at_xxxxxx [mailto:systemsafety-bounces_at_xxxxxx RICQUE Bertrand (SAGEM DEFENSE SECURITE) Sent: 05 March 2015 10:48
To: Peter Bernard Ladkin; Nick Tudor; The System Safety List Subject: Re: [SystemSafety] Degraded software performance [diverged from Fault, Failure and Reliability Again]

As a member of the maintenance team, my opinion is that :

Annex D is for the moment poorly related to the body of the standard: i.e. the standard does not account for probability of failure of software as a design input or as a performance objective for new software. The issue seems only relevant, for the moment for existing software associated with the intention to "reuse" it.

The question of the intended scope of applicability of a quantification of software performance based on probabilities thus arises. Limited to "reuse" or extended to "new". This will have to be clearly stated somewhere.

It will be difficult to do some progress if we are not able to agree on: * Do we consider software without hardware ? Which is the mainstream of the existing standard.
* If we think it is not relevant to segregate HW and SW, is it realistic to foresee the consequential modifications we would have to implement in part 1 and 2 of the standard ?
* Are we measuring:

     *an intrinsic property of the software (failure rate or probability)?
     *a property of the software development process (quality of the
requirements, quality of the tests)?
     *a property of the SW/HW integration ?
     * an aggregate property of all of the above ?

Bertrand Ricque
Program Manager
Optronics and Defence Division
Sights Program
Mob : +33 6 87 47 84 64
Tel : +33 1 58 11 96 82

-----Original Message-----
From: systemsafety-bounces_at_xxxxxx [mailto:systemsafety-bounces_at_xxxxxx Peter Bernard Ladkin
Sent: Thursday, March 05, 2015 11:24 AM
To: Nick Tudor; The System Safety List
Subject: Re: [SystemSafety] Degraded software performance [diverged from Fault, Failure and Reliability Again]


I do think we need to be clear about the situation with IEC 61508 Part 7 Annex D.

On 2015-03-05 10:41 , Nick Tudor wrote:
> .. There is a plan to
> update a standard IEC61508 with material about how one might use
> software reliability in safety systems.

There is a plan to update a 17-year-old section, Part 7 Annex D, about statistical evaluation of software in IEC 61508.

> Standards are supposed to represent the consensus of the community and
> it has been reported by others on this list that many standards do not
recognise this approach.

The new version of IEC 61508 will represent the consensus of the Maintenance Team charged with updating it, and the vote of approval from participating national committees.

If we don't fix Annex D in the forthcoming maintenance cycle, it will stay the same as it is now; I doubt very much if it will be deleted.

I'm just one person. I would imagine there are 25-30 active members of the maintenance team, some of whom are on this list.

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

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