Re: Is there an XSLT/XPath processor good enough to us

Therebs always reasons for software to have faults.  An early example from
the late b60bs is something I did.  Herebs the story.

I was taking a course on machine architecture and programming, and we had an
exercise writing an IBM 360 assembler program.  I forget what the program was
supposed to do, but I wrote it and submitted it for running overnight as was
the case in those days.  Next morning I was called into the Computer
Centerbs office and got a serious tongue lashing for having destroyed all
the output produced by all the programs run on the Universitybs computers
the previous day.

It turns out that what happened was the following:
1. I had mistyped b4b instead of b3b (or maybe the other way around)
in one column of one of my punch cards.
2. My program crashed and the computer proceeded to do a program dump.
3. The usual very small print line limit for student programs was ignored for
program dumps, on the theory that you really want to know what went wrong.
4. The effect of my mistyping was that a method/function stack frame was
linked to itself as its own bparentb.  So there was an infinite length
print out.
5. The disk software assumed that the original small limit on how much output
a program produced was still in effect, and had no check on exceeding the
capacity of the disk drive.
6. The disk filled up and the system kept trying to write.  The system
crashed.
7. The computer staff (itbs now about 2am in the morning) rebooted the
system and it crashed again: the disk drive software was corrupted at this
point.
8. After a few attempts at that, they finally reformatted the disk, and
rebooted the machine.  And all the output on that disk was lost.

The thing is, that there were two conflicting assumptions made in the design
of two separate pieces of system software.  And otherwise smart people
hadnbt thought about such a conflict.  The further assumption that an
undergraduate should never make a typo compounded the problem.  I forget what
they eventually did: I think checks were added.  Their first idea for a
solution was to not let me run any more programs on the computer, but they
fortunately rethought that one. At the time I didnbt think that I was the
culprit.

The point is that large systems are always made up of multiple components,
made by multiple people, with multiple assumptions.  And therebs always room
for error.  That said, a lot can be done about that, and errors minimized.
But they are intrinsic to how things work.

Sam.

------------
Sam Wilmott
sam@xxxxxxxxxx
www.wilmott.ca

bWe have met the enemy and he is us.b b Walt Kelly