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From: Ken Garlington <kennieg@flash.net>
Subject: Re: Critique of Ariane 5 paper (finally!)
Date: 1997/08/29
Message-ID: <3406B759.19@flash.net>#1/1
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Organization: Flashnet Communications, http://www.flash.net
Reply-To: Ken.Garlington@computer.org
Newsgroups: comp.lang.ada,comp.lang.eiffel
Date: 1997-08-29T00:00:00+00:00
List-Id: <comp.lang.ada>


Jeff Kotula wrote:
> 
> Robert Dewar wrote:
> 
> > <<I think one of the primary differences between correctness and
> > reliability is
> > that the former can be defined crisply while the latter cannot.>>
> >
> > No, I disagree, these are completely different qualities, they are
> > related,
> > but as I said earlier, you can have reliable programs that are not
> > correct, and correct
> > programs that are not realiable.
> 
> This is a nonsensical statement. In the first case, you will have a
> program
> that reliably does the *wrong* thing,

Exactly. Note that you used the word "reliable" to describe a reliable
program. Thus, it must be reliable!

> and in the second case, you
> will have a program that doesn't do the right thing all the time.

However, "correct" is not the same as "does the right thing".
Presumably,
"corrects" means "conforms to some testable definition of requirements."
A "correct" program may not be reliable, however, if used in some
context not anticipated by the requirements, for example.

> Neither of these cases is of any interest to the goal of creating
> high quality functioning software.

Actually, _both_ are of interest in terms of quality, as are "safe"
(which is something different from either reliability or correctness),
"portable," "maintainable," etc.

More to the point, it is critically important not to confuse these
attributes, since they (as Dr. Dewar has noted) are not synonyms.