Re: Papers on the Ariane-5 crash and Design by Contract

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Jonathan said

<<I've heard at least one other person claim that if you add up the cost
of saving 2 bytes per date across millions of instances, multiply by the
much higher cost of data storage in the past, and allow for inflation,
then the amount saved is actually more than the cost of solving the year
2000 crisis.
>.

  Claims like this are almost always just guesses that have been passed
  on, and because they appeal to the hearer (as in this case :-) they
  get passed on further. This particular one is nonsense. Just do the
  calculations yourself very roughly and you will see.

<<How far do you think that an aircraft engineer would get with a proposal
to increase safety and efficiency at a cost of "only" 10% more weight?
That's the difference between an aircraft flying and an aircraft failing
to take off.  Sometimes you just have to work within a short-term budget,
and make the best choices you can under the circumstances.
>>

  I sure don't think that that engineer would be treated kindly when he
  had to explain that the reason that a plane fell out of the sky and
  killed x hundred people was to save 10% of the weight so that more
  passengers could be carried.

  Again, this 10% of the weight figure is pulled out of thin air. Care in
  software usually weighs nothing. Often carefully written and safer software
  can be shorter than carelessly written unsafe software.

  Actually talking about the weigh of the software reminds me of the old
  story (fact? urban legend? who knows, perhaps the appropriate urban legend
  www site knows). The story goes that on an early NASA mission, the engineer
  in terms of the weight control demanded to know the weight of the software.
  He would not take for an answer that it had no weight and demanded to see
  it. Finally he was shown a deck of punched cards. "Ah ha!" he said, "see,
  I knew it had to weigh something". The software engineer replied: "You
  don't understand, the software is the *holes* punched into these cards :-)

P.S. rumours can often be turned into fact due to wishful thinking. Try 
starting a rumour based on a completely bogus fact, and present it to 
someone to whom it will appeal. For example, tell an environmentalist
"Did you know -- 24% of the volume in land wastes is taken up by
non-degradable plastic!". Or tell someone of suitable political
persuasion "Did you know the Russians are building ICBMS faster than
ever, and that now they have three times as many deployed than the
time when communism supposedly disappeared", or or or or [[make up
your own attractive pseudo-fact here]] :-)