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

[SPRIGGS, John J]

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 lists.techfak.uni-bielefeld.de] On Behalf Of Peter Bernard Ladkin
Sent: 16 March 2016 07:23
To: Les Chambers; systemsafety at lists.techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] Modelling and coding guidelines: "Unambiguous Graphical Representation"

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