Frank,
> > What do you mean by understand? I would guess you would claim that
> > people can have complete knowledge of the semantics of a program.
>
>Your guess about what I mean is not germane, since I'm not the one claiming
>that understanding might not exist, and indeed sounds a little like a
>straw man, if you'll forgive my directness.
>
>As it happens, I would never claim that people can have *complete* knowledge
>of anything very much. However, since I certainly don't think that
>understanding is an all-or-nothing proposition, I don't see this as a problem.
I think this issue has partly arisen because of our various interpretations
about
what the term 'program understanding' means. To me it implies:
1) that it possible to know everything about a program. Now there are
people who claim to understand programs in this sense. Pointing
out holes
in their knowledge, apart from making them irate, often results in them
defining bounds to what needs to be understood. The correct
response, in
mine (and I think yours) view is to agree that there are levels of
knowledge.
2) being able to build a coherent, simple model of how things fit together.
Perhaps this is idealism on my part, or my love of physics coming
through
(ok, so subatomic physics is not very simple or coherent at times).
I agree with Thomas that we need to promote the idea of programmers having
islands of knowledge. All we need is a term to describe it...
>In something as complex as a computer system, *complete* knowledge of the
>semantics of a C program might oblige me to apprehend everything from
>its effect on the CPU's registers to the consequent changes in ambient
Not so. C along with most languages is defined behaviour in terms of an
abstract machine. No real world constructs need be invoked (but it is
useful for understanding why things are defined the way they are).
The C specification is a knowledge base like any other and there are
experts who know their way around it better than non-experts.
>However, it seems to me that you are defining 'understand this C program'
>as 'predict the consequences of compiling and running this C program in
>an unspecified environment, with no opportunity to find out more, and with
>an obligation to be 100% correct and 100% comprehensive.'
Guilty as charged. But then I do work in a very unusual environment and
I do mix with people who have the same outlook (in fact some are worse than
me).
> As a corollary
>to my earlier remarks, this would be a pointless definition.
It has its uses, or so we all keep telling each other :-)
>Arthur seems to be doing the same thing here when he says:
Arthur. You may have meant to send to Frank only (the default behaviour
is for this list reply to respond to the sender, not the list), or reply is
still
working its way through my ISP (I sometimes get replies to what I post
before I see my own posting).
>It seems likely to me that you both *do* understand what the program does,
I only claim to be able to provide an interpretation of the likely external
effects (what you will see on the screen) of compiling and executing this
program within a certain class of computing environments.
I would claim that I understand what you want me to say when you
present me with this program (but that is probably because I don't know
as much about psychology as I do about the C abstract machine).
derek
--
Derek M Jones tel: +44 (0) 1252
520 667
Knowledge Software Ltd mailto:[EMAIL PROTECTED]
Applications Standards Conformance Testing http://www.knosof.co.uk
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