Re: Critique of Ariane 5 paper (finally!)

[Bertrand Meyer <Bertrand.Meyer@eiffel.com>]

Professor Robert Dewar wrote that my argument

> seems over-facile and rather academic 

Wow! But I'll choose to take "academic", coming from
a .edu address, as a compliment. And "over-facile"
might refer to how easy the basic ideas of Design
by Contract are to teach and implement.

He adds that what he calls my "jump from sufficient to
necessary" 
 
> can only be regarded as advertising puffery.

Advertising puffery! Delightful choice of words.
Now this is a solid technical rebuttal. But here is the
explanation:

> [I]t is clear that you [i.e. me, BM] are not disinterested
> in the claim!

OK, finally things are clear. When everything else fails, resort
to questioning the other person's integrity: I have a vested
interest in seeing Eiffel succeed -- that explains it all.
(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.)
 
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. 

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".
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. How many more Ariane-like failures do we
need?


-- 
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 ==