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From: Ken Garlington <GarlingtonKE@lmtas.lmco.com>
Subject: Re: Papers on the Ariane-5 crash and Design by Contract
Date: 1997/03/24
Message-ID: <3336CC41.7FE7@lmtas.lmco.com>#1/1
X-Deja-AN: 228004765
References: <332B5495.167EB0E7@eiffel.com> <tz8ohcjv7cc.fsf@aimnet.com>
Organization: Lockheed Martin Tactical Aircraft Systems
Newsgroups: 
 comp.lang.eiffel,comp.object,comp.software-eng,comp.programming.threads,comp.lang.ada
Date: 1997-03-24T00:00:00+00:00
List-Id: <comp.lang.ada>


Ulrich Windl wrote:
> 
> Again, I was not stating that the code after the first detected error
> is still valid, I was just saying "you might turn on fuzzy mode if you
> must go on". Fuzzy mode might be wrong (lead to wrong results).

The problem with this approach is:

1. There might not be a fuzzy mode. Feedback systems are notoriously
difficult to control with invalid inputs.

2. Any fuzzy modes have to be specified, designed, implemented,
processed
by the compilation system, and tested. This all takes resources, and
makes
it possible to introduce an error. A more complicated system is not
necessarily a safer one! As a design guideline, simpler is better
(although
there are many exceptions to that rule).

> 
> If you have an algorithm that is performing in a limited window of
> time, it would be an advantage if the equipment were still together
> after the algorithm's time is over. Agreed, with rockets you just
> don't have enough fuel to do a course correction later.
> 
> [...]
> 
> Ulrich

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