Re: Ada noob here! Is Ada widely used?

[tmoran@acm.org]

>is that it presumes that states are random, which are not, because [most
>of] programs are deterministic. Any randomness which might exist is derived
>from the inputs. I.e. it is the program usage, which makes the *same*
>program less or more reliable. According to this approach the most reliable
>car is one you do not drive.
  Mechanical devices also fail due to unfortunate, unanticipated,
combinations of random inputs.  Rockets don't fail in the middle of the
night sitting in the assembly building.  They fail when, for instance, the
air temperature is very low and the rocket is on full thrust and with
those inputs the O-ring can't sufficiently do its job.  You don't say
"O-rings are or are not reliable" - you say "under such and such
conditions O-rings are 99.9999% likely to prevent dangerous amounts of
leakage.  Under such and such other inputs, that drops to 99.9%,
or 90%, or 10%."

> ... E.g. Let I modify 0,01% of the source of 90%
> "reliable" program. I can tell nothing about whether the result is 90%
> reliable +/- factor * 0.01%. This model just does not work.
   The word "model" is key.  It is meaningless to talk about whether
something, software or hardware, *is* stochastic - but one can observe
whether a stochastic *model* of the system is helpful or not.
   As to program changes, one talks about how confident you are that the
program will not hit a bug today, as compared to yesterday before you made
the change.  Your confidence will depend not just on the fraction of
source code changed, but also on careful consideration of the nature and
expected effects of the change, and observations while testing the changed
version.