Re: Ariane Failure

["Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org>]

I beg to differ on the "Bad Directions" part. Note that the software in
question was designed for the Ariane IV which had a different flight
profile. The FDA thinking for the module in question went sort of like this:
"Any number that shows up here big enough to generate a hardware overflow
interrupt has got to be so far out of the flight profile that it would most
likely indicate a bad sensor. The accommodation for this failure should be
to transfer control to the other side where we might still have a good
sensor..." This logic worked fine in Ariane 4 and would likely have detected
a sensor failure and accommodated it appropriately. In my mind, that sounded
a lot like "Good Directions" :-)

The problem arose when the assumption was made that software that was
designed for Ariane 4 and that worked just fine in that environment was
therefore fit to fly Ariane 5 WITHOUT being tested and validated against the
Ariane 5 flight profile. That's a pretty basic and fundamental error that
goes well outside the realm of control of a programming language or
methodology.

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com


"Richard Riehle" <richard@adaworks.com> wrote in message
news:3CA4B8E5.72909C9B@adaworks.com...
>
> The problem with Ariane V begins with Systems Engineering management.
> The decisions about what to do when an exception occurs were wrong, and
> not tested.    Although Design By Contract might have helped,  I doubt
that
> Eiffel would have been appropriate because of other issues related to
> Eiffel.   I like Eiffel, but don't consider it appropriate for a project
such
> as Ariane V.    The SPARK approach to Design By Contract (they don't
> call it that, but that is what it is)  could have worked well, especially
> since it was programmed in Ada.   By the way, the Ada code worked as
> it was directed to work, but it was given bad directions.
>