Re: Critique of Ariane 5 paper (finally!)

[Ken Garlington <kennieg@flash.net>]

Bertrand Meyer wrote:
> 
> (Doesn't explain, though, why so many other contributors have
> expressed agreement with the analysis of the Jezequel-Meyer
> Ariane paper and support for Design by Contract.)

How many of them build safety-critical real-time systems? None
who support DBC have indicated experience in this field. Thus,
my explanation is simple: they have insufficient experience
to judge the likely pitfalls in the application of DBC to a domain
they (and, I assume, you) don't understand.

Your case seems to be somewhat less strong among the actual
practitioners in the field. Coupled with the apparent lack
of Eiffel applications in the domain under discussion, your
appeals to authority (random Eiffel users on Internet?) aren't
all that compelling.

> This is a slippery path to follow since very few people
> can claim to be "disinterested". So are Robert Dewar and
> I  going to spend the next three months arguing who is the most
> unbiased? No, no and no. I won't be dragged down to that level
> and will just assume that the line quoted above was a
> regrettable slip of the pen.

On the other hand, _I_ have absolutely no vested interest in
either promoting Ada or attacking Eiffel; nor do I have any
interest in defending the Ariane 5 team. I do have an interest
in using new technologies in the domain in which you have
taken a sudden interest, and would like to understand how
it could help. However, my concerns have been uniformly
unaddressed through any sort of technical argument.

I notice that both you and Mr. Jezequel have a strong desire
to uncover "vested interests." When I first joined this
discussion, he assured me that my job as a software test
engineer would not be eliminated by a switch to DBC. Since
I'm not a software test specialist, this was a strange
statement to make, to be sure. :)

So, other than some perceived bias of practitioners against
"the next big technology." as I believe you indicated in
a previous post, what is the bias that practitioners such
as myself, Mr. Kohl, and Mr. White have against DBC (other
than the obvious one -- we won't use a technology whose
authors are so emotionally involved in their quest that
they are insulted by the mere suggestion of contrary views)?

> The "necessary" condition is simple: you won't get reliable
> software unless you take care to associate specifications --
> contracts -- with software elements, especially reusable
> components. You can then use these contracts to build
> the software, to document it, to validate it statically,
> to test it (if you have support for run-time monitoring,
> as in Eiffel), to control the proper use of inheritance,
> to discuss the software within the software team as well
> as with management, customers, users and regulatory agencies.
> Anyone who has used the approach knows that it dramatically
> improves the quality of the product and the process.
> And it's not even an expensive technique.
> 
> No one ever said Design by Contract was "sufficient".

Other than youself, in your Ariane 5 paper.

Perhaps it's a problem of the English language; but "probably yes"
certainly translates as "sufficient" in my understanding.

> My "Object-Oriented Software Construction, 2nd Edition"
> (Prentice Hall) has a 9-page section (11.14, pp. 398-406)
> discussing its limitations. But to encourage developers of
> mission-critical software to ignore this powerful tool is
> irresponsible. 

This is really the true irony. Several practitioners have
invested a great deal of Internet time _not_ ignoring this
technology. We have tried to understand why it would help in
our domain; have tried to draw the Eiffel experts into a
technical discussion of its strengths and weaknesses, and
have generally been told

  -- we don't understand our own products
  -- we don't understand software engineering
  -- we are biases against new ideas

I wonder why there aren't more Eiffel projects in this
domain? :)

Mr. Jezequel and Mr. Meyer have both indicated they
have no interest in pursuing any discussions on this
subject. Isn't this the same as irresponsibly discouraging
the use of DBC?

>How many more Ariane-like failures do we
> need?

No more. This is why we need a balanced budget immediately!
(Why not? If I don't have to show that a balanced budget
would have prevented the problem, it's an equally important
claim!)

> 
> --
> Bertrand Meyer, President, ISE Inc., Santa Barbara (California)
> 805-685-1006, fax 805-685-6869, <Bertrand.Meyer@eiffel.com>
> Web: http://www.eiffel.com, with instructions for free download
> == ISE Eiffel 4: Eiffel straight from those who invented it ==