Information Technology Reference
In-Depth Information
Chapter 14
Modelling Styles
\What kind of world do these people live in?" Claire asked. They were
still sitting in the back row of the lecture theatre, but most of the audience
was already filing out. A small group at the front were gathering round the
speaker, still carrying on a heated discussion. Alex grinned. \Didn't you like
it? I thought he made a good case." \But what use is it? I mean, does it
matter whether we distinguish between something being necessarily necessary,
or just necessary? And when he said `In a world with no future, everything is
necessary,' I really wondered what the point of it all was."
At Alex's suggestion, they had come up to the University, on the hill
overlooking their oce, to listen to an inaugural lecture in the Computing
Department by the new Professor of Modal Logic, who was well-known for
applying his theoretical ideas to industrial problems. He had talked about
the importance of putting modelling on a formal basis, illustrating his argu-
ment with examples of how simple statements about requirements could be
interpreted in many ways.
\I'm still not sure if some of the subtle points really matter," Eleanor added.
\Can't they be sorted out by applying common sense?" \Well," Alex thought
for a moment before continuing, \a lot depends on what sort of cooperation
we are trying to support. If we are all sitting round a table talking about
a problem, any differences in the way we look at it can probably be sorted
out as we go, but if we are writing down a design for others to interpret,
it's not so easy. And it really gets to be important when we start trying
to automate things, particularly if the misunderstandings are about how the
languages we use are supposed to work." \But that's why we use standardized
languages, isn't it? Surely languages like Java are universal these days?" \Not
really, Claire; they are not as formally based as you might think, and the
real problems come when we look at languages that deal with requirements
and rules of behaviour. A statement that setsbtoa+ 1 is generally well
understood, but one that says the customer ought to pay within seven days
is much more dicult to be sure about. The closer to the real world we get,
the more dicult it is to be precise about how all the tricky cases are to be
handled. That's why the lawyers rely on the idea of the reasonable man and
what such a man might do | it gets them out of a lot of dicult detail in
predicting all the possible situations. Our tool builders can't do that."
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