From: Tom Cloyd <tomcloyd@...>
Date: 2008-04-18T13:54:48+09:00
Subject: Re: Ada vs Ruby

Phillip Gawlowski wrote:
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> Rick DeNatale wrote:
>
> |
> | Yes, testing, not a blind faith in whatever language is being used,
> | and it's compiler.
>
> Indeed.
>
> |>  Anyway, this problem is (AFAIK, anyway), countered by using redundant
> |>  implementations of the hardware and software (well, as far as 
> possible,
> |>  anyway), to minimize the effect of unknown states.
> |
> | Of course this isn't perfect either.  In fact "The Bug Heard Round the
> | World." which I mentioned earlier in this thread, was a failure of
> | redundancy.
>
> Perfection is an ideal, that we can only approach asymptotically, never
> achieve (since we, as human beings, aren't perfect).
>
> | Of course all of this worked well during the pre-STS1 mission sims.
> |
> | However, on the day of the launch, there was a clock skew between the
> | redundant computers, so the output from one lagged just a bit behind
> | the others, and the system halted the launch, unnecessarily as it
> | turned out, at T-3
> |
>
> That is it was an unnecessary halt is probably the benefit of hindsight.
> Unfortunately, I can only assume that it was so, since I cannot find a
> free version of the paper you linked to earlier.
>
> Without the benefit of hindsight, the problem of the skewed clocks could
> have a much wider impact than it actually had, masking deeper problems
> of the software and / or hardware used.
>
> In such a case, we enter the area of risk management: Is it worth to
> risk the whole mission on something that hasn't been done before at this
> scale? While there was knowledge, at the time, of space flight thanks to
> the Apollo and Mercury programs, something like the Space Shuttle was
> new, and very different from the "throw away" capsules used before, with
> different approaches to solve the problem of getting something into
> orbit and back again, preferably all in one piece.
>
> With the lives and money at stake with the Shuttle program, the decision
> to cancel was wise, IMO, even though it turned out to be unnecessary.
>
> One could even claim, that the systems performed as planned, and
> prevented a catastrophe. Without actual empirical testing we probably
> won't know for sure, and can only speculate.
>
>
> In the end, though, this shows that no amount of software nor hardware
> can replace judgment calls made by human beings. Technology can only
> assist in making decisions. And in the cases where humans cannot make
> decisions (like a Shuttle launch, where automation has to be used), a
> use of technology (and not just languages and compilers and processes)
> still requires humans for the get go.
>
> I think that the movie Wargames touched on this topic in a good, and
> decent, way, as well as Crimson Tide (in a not very related way, though,
> but it demonstrates my point of not putting too much trust into process).
>
> - --
> Phillip Gawlowski
> Twitter: twitter.com/cynicalryan
>
"...no amount of software nor hardware  can replace judgment calls made 
by human beings. Technology can only
assist in making decisions."

For what it's worth, in my profession (clinical applied psychology/ 
psychotherapy), it's written into our professional ethics that decisions 
are always to be made by people, not by some testing device, instrument, 
or technology. Sometimes we merely review and approve, but that human is 
required to be there. Very few people object to this, especially after a 
little reflection.

Cross-validation of process, eh?

t.


-- 

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