[SystemSafety] Proven use software and software quatitative reliability

[RICQUE Bertrand (SAGEM DEFENSE SECURITE)]

The normal framework in system + SW production (as well under IEC61508 as ARP/DO) is:

·         Assign a DAL/SIL

·         According to this DAL/SIL comply with requirements

·         The SW is then deemed to be compliant with this DAL/SIL and possess the associated properties

·         The system also at another level



Some remarks on this framework:

·         There are lot of requirements

·         Probability of failure is only one among others

·         Integrity is an important property

·         Probability is (almost) the single one which is not required for SW



Framework for proven in use :

·         Observe the system including the SW as a package

·         Count the failures

·         Extrapolate a probability of failure / reliability FOR the SW alone

·         Deduct the guaranteed DAL/SIL



I wonder in which metaclass of fallacies enters this reasoning.



How can one deduct properties of a SW by observing AT SYSTEM LEVEL a parameter which is the single one that is not a design parameter of the said software ?



Bertrand Ricque

Program Manager

Optronics and Defence Division

Sights Program

Mob : +33 6 87 47 84 64

Tel : +33 1 58 11 96 82

Bertrand.ricque at sagem.com




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