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From: Ken Garlington <GarlingtonKE@lmtas.lmco.com>
Subject: Re: Papers on the Ariane-5 crash and Design by Contract
Date: 1997/03/26
Message-ID: <333963D1.77F8@lmtas.lmco.com>#1/1
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References: <332B5495.167EB0E7@eiffel.com> <tz8ohcjv7cc.fsf@aimnet.com>
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Organization: Lockheed Martin Tactical Aircraft Systems
Newsgroups: 
 comp.lang.eiffel,comp.object,comp.software-eng,comp.programming.threads,comp.lang.ada
Date: 1997-03-26T00:00:00+00:00
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Thomas Beale wrote:
> 
> Jean-Marc Jezequel wrote:
> >
> > Yes this is true. But, since the SRI was reused from Ariane4, the problem
> > is not with developers, but with the *integration* team.
> 
> If the SRI is a black box, and this is taken to mean it is reusable,

I've never considered the term "black box" to be synonymous with
"reusable
in all environments." Moving away from software, a black box built for
any
Air Force aircraft may not meet the environmental conditions required
for
a Navy aircraft.

> doesn't
> that imply (by definition) that it should do its job with _any_
> trajectory
> data (or at least any data for a "reasonable" rocket trajectory)?

Once you use the word "reasonable," you have opened the door to
a potential problem.

 If
> this
> is not true, then you haven't got a "reusable SRI", you have "Ariane-4
> SRI".
> 
> So the assertion that the "real problem" was the decision not to supply
> Ariane-5
> trajectory data relies on the idea of the SRI not really being a
> reusable component,
> but one that "might work" or something similar.
> 
> However, the fact that an explicit decision was made not to use this
> data in effect
> means that the deciders (whoever they were) tacitly deemed the SRI as
> reusable (whether
> they realised that or not). (One imagines that this would be true for
> all kinds of
> components on the Ariane-5....).
> 
> So it seems that the "real problem" was one of the following:
> 
>         * the SRI component being deemed (knowingly or unwittingly) as reusable
> when it
>           wasn't, and then the development proceeding as if it was a reusable
> component.
> 
>         * if the SRI component was indeed _supposed_ to be re-usable, meaning
> it should have
>           worked with different datasets (among other things), then the fault
> is in the
>           implementation of the SRI's notional engineering specification, i.e.
> its "contract"
>           to other components.
> 
> So either way, it is a re-use error, as originally claimed.

I don't think anyone has suggested otherwise?


> 
> - thomas beale

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