Re: Trust but verify (was Re: Papers on the Ariane-5 crash and Design by Contract

[jws@tiac.net (Jeffrey W. Stulin)]

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Hi there:

As my father is fond of saying "You�ve got to play the percentages." By 
this he simply means that while nothing in life is guaranteed, it is 
still a good idea to attempt to arrange matters to give them the best 
opportunity of working out in your favor. And that is the answer to 
Ken�s questions.

If the Ariane software engineers had the reuse mindset, NOT the specific 
mechanisms of Eiffel, but the design by contract reuse mindset, then 
they MAY have written the assertion, and MAY have noticed, while 
integrating the modules, that the assertion would not have been met.

I often specify "impossible" assertions because, human nature being what 
it is, the impossible will happen, and it is exactly these non intuitive 
circumstances which cause the most trouble.

Now 95% of what Ken has stated about testing and so forth is perfectly 
correct. And indeed there is no guarantee that the MAYs above would have 
come to pass. However, it is not unreasonable to speculate that if the 
integrators had been trained with emphasis on the problems of reuse, the 
specification error might have been found. Perhaps likely to be found is 
a bit strong, but I don�t find that stretch much of a sin.

 Furthermore, the papers primary between-the-lines claim, that we better 
learn a reuse mindset since we are (finally) entering the age of 
software reuse, and that the penalties for a reuse error could be 
disastrous, is not a stretch at all. It is simple common sense.

I also find little fault with the implied notion that Eiffel is the 
language which would have had the best chance of finding this particular 
error. My reasoning is simple:  Eiffel is a thin surface for an idea, 
the idea of how to specify and reuse software (design by contract etc.). 
That�s what Eiffel is. Now there may be many areas where Ada would have 
strengths in solving problems and Eiffel would fall flat on its face. 
But not on issues of software reuse. Eiffel is simply the best.

Finally, I have no problem with Ken�s Putting BM & Co. feet to the 
flames. I enjoy seeing ideas stress tested and especially enjoy reading 
about the practical view of those involved in a particular industry. I 
do, however, object to Ken�s tone in some of his postings. As a reader I 
feel that I am being shouted at, and I don�t like it. Please keep 
posting Ken, but post calmer.


Thanks,

Jeffrey W. Stulin