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RE: The Airplane Example (was Re: StreamingXML)

• To: "Amelia A Lewis" <amyzing@t...>,"Dare Obasanjo" <dareo@m...>
• Subject: RE: The Airplane Example (was Re: StreamingXML)
• From: "Michael Rys" <mrys@m...>
• Date: Tue, 4 Jan 2005 20:12:42 -0800
• Cc: <xml-dev@l...>
• Thread-index: AcTyyJHwajFa7zavRe6e4sQpe2lGdAAEq72Q
• Thread-topic: The Airplane Example (was Re: StreamingXML)

> Sure.  Dynamically typed languages aren't going to have the overflow
> error in the first place.  Now, the overflow error was in a function

Overflow errors are dynamic errors and may or may not occur regardless
of the typing semantics (it depends on the casting semantics whether you
error, truncate or roll-over). 

Static type errors are discovered at compile time and avoid such
problems (assuming the programmer carefully resolves the issue).
Strongly and dynamically typed languages do indeed raise type errors,
just at runtime. Weakly typed systems (regardless of whether they are
static or dynamic) would have attempted a cast (and then the casting
semantics would determine the outcome).

Could we please use the right terminology for the different typing
approaches? (see
http://sqljunkies.com/WebLog/mrys/archive/2004/05/13/2480.aspx for a set
of useful definitions)

Best regards
Michael

> -----Original Message-----
> From: Amelia A Lewis [mailto:amyzing@t...]
> Sent: Tuesday, January 04, 2005 5:43 PM
> To: Dare Obasanjo
> Cc: xml-dev@l...
> Subject: Re:  The Airplane Example (was Re: 
> StreamingXML)
> 
> On Tue, 4 Jan 2005 17:29:27 -0800
> "Dare Obasanjo" <dareo@m...> wrote:
> 
> > > -----Original Message-----
> > > From: Amelia A Lewis [mailto:amyzing@t...]
> > > Sent: Tuesday, January 04, 2005 5:17 PM
> > > To: Daniela Florescu
> > > Cc: xml-dev@l...
> > > Subject: Re:  The Airplane Example (was Re:
> > >  StreamingXML)
> > >
> > > Actually, according to the full report:
> > >
> > > http://sunnyday.mit.edu/accidents/Ariane5accidentreport.html
> > >
> > >
> > > In other words, because of strong typing and exception
> > > handling in Ada, Ariane 5 crashed.
> >
> > That's not the conclusion I came to from that report. Can you
explain
> > how weak typing [or dynamic typing which was the original point of
the
> > thread] would have made this problem any better?
> 
> Sure.  Dynamically typed languages aren't going to have the overflow
> error in the first place.  Now, the overflow error was in a function
> which was redundant to flight operation, but because it occurred and
was
> not handled, the software was designed to shut down the processor.
When
> the second processor tried to shut down, it couldn't, because of
another
> function requiring that its backup (which had already failed) be on
> line.  So it dumped core (sent diagnostic data to the main computer),
> which was interpreted as altitude information, which in turn caused a
> major course-correction burn to be initiated (in error, since the
> diagnostic data wasn't altitude data), causing the vehicle to begin to
> disintegrate, causing the range safety to trigger the self-destruct.
> 
> What it *wasn't* was a type casting error.  Not in bloody Ada; it's
> *not* a weakly typed language that would *permit* a typecasting error
of
> that magnitude.  Among the bondage and discipline languages, Ada
stands
> out as a laughing sadist.  A dynamically typed language would have
> determined that the integer was bigger than sixteen bits (not that it
> mattered much, since the function that went gronk was part of the
> alignment reset function, inapplicable to Ariane 5).
> 
> The key is that it was the throwing of the error that caused the
> processor to shut down.  If the processor had ignored the error
(because
> the language didn't have exception handling, for instance, or because
an
> error wasn't thrown) the flight would have continued.  That the error
> had nothing to do with flight is merely ironic, at that point.
> 
> > I think the report vindicates Dana's position.
> 
> I'll just disagree, then.  The authors of the report also tend in that
> direction, since their solution is to increase the rigor of typing,
> exception handling, and testing, but they *also* specify that the
> processor should not shut down (should provide "best available" data)
in
> the face of an error.
> 
> Amy!
> --
> Amelia A. Lewis                    amyzing {at} talsever.com
> "Oh, [expletive deleted]!  You did it just like I told you to!"  (The manager's
lament)
> 
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