On Wed, Apr 16, 2008 at 6:23 PM, Eleanor McHugh
<eleanor / games-with-brains.com> wrote:
> On 16 Apr 2008, at 14:42, Phillip Gawlowski wrote:
>
> > I doubt, however, that there is a single undefined state in the Space
> > Shuttle's software. No uncaught exception, no reliance on language
> > features to do the right things, but well understood and diligent
> > implementation of those, together with rigorous QA.
> >
>
>  It's a lovely idea, but ponder the impact of Göäel's Incompleteness
> Theorems or Turing's proof of the Halting Problem. In practice there are
> program states which can occur which cannot be identified in advance because
> they are dependent on interactions with the environment, or are artefactsf
> the underlying problem space.
>
I am not sure but on a first approach I believe that neither Göäel nor
Turing apply because they are talking about systems describing
themselves. IIRC it is a theorem in TNT(1) making an assumption about
TNT in the first case and a turing machine reading the description of
a turing machine on its tape in the second case.
I do not believe that Aircraft Control Systems have this degree of
self awareness, but I can stand corrected if I am wrong, because
although I have been taught a lot about TM and TNT I do not know a lot
about Aircraft Control.

>  That's why run-time error handling and fail-safe behaviour are so important
> regardless of the rigour of Q&A processes.
That however I agree with!

(1) http://en.wikipedia.org/wiki/Typographical_Number_Theory
Cheers
Robert
-- 
http://ruby-smalltalk.blogspot.com/

---
Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein