Re: [SystemSafety] Modelling and coding guidelines: "Unambiguous Graphical Representation"

From: Matthew Squair < >
Date: Thu, 17 Mar 2016 23:44:54 +1100


Strangely that COTS low number has been 'used in anger' on a project of mine. Any idea were it came from?

Matthew Squair

MIEAust, CPEng
Mob: +61 488770655
Email; Mattsquair_at_xxxxxx
Web: http://criticaluncertainties.com

> On 17 Mar 2016, at 9:23 PM, SPRIGGS, John J <John.SPRIGGS_at_xxxxxx >
> Peter wrote: "... let me refer you to the current edition of IEC 61508, Parts 2 and 3. The conditions on "proven in use" for SW are to my mind incoherent. "
>
> IEC61508 is not alone in being incoherent on this matter, EUROCAE Document ED-109 (RTCA/DO-278, if you prefer) sets assurance levels on the basis of the severity of the risk that is being mitigated but, in a note about using service history to support assurance for COTS and the like, it suggests a (low) numbers of failure-free hours that can be used to claim achievement of some assurance levels. But, surely, that is "likelihood", which should be orthogonal to severity.
>
> The newer version, ED-109A (RTCA/DO-278A) does not have this note, which may be why some have said that the COTS requirements are much more onerous than in the original...
>
>
> John
>
> -----Original Message-----
> From: systemsafety [mailto:systemsafety-bounces_at_xxxxxx > Sent: 16 March 2016 07:23
> To: Les Chambers; systemsafety_at_xxxxxx > Subject: Re: [SystemSafety] Modelling and coding guidelines: "Unambiguous Graphical Representation"
>
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systemsafety_at_xxxxxx Received on Thu Mar 17 2016 - 13:45:26 CET

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