Information Modeling

Peter Kitson

ISBN : 0134577485

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Why Compute?

What are computers for? What is their purpose? Suppose your life depended upon coming
up with a word or phrase that most accurately summed up what computing is all about.

What would your answer be?

Would you say that computing is about
sex?
drugs?
rock\'n\'roll?

No, there\'s not too much of that in computing.

Well then, perhaps it\'s about

money?
power?
food?
gambling?

No, these topics are hardly ever discussed in computing magazines.

This is surely most regrettable. Does this mean that, if we take out all the interesting things
in life, computing is about what remains? Not quite, we hope!
Computing is concerned with taking the interesting things out of life and representing
them somehow. It is all about modeling. Everything inside a computer is a representation
of something else.

Facts and Knowledge
Suppose we got together and tried to describe all the things we know about some orga-
nization and its environment. The organization need not necessarily be a commercial or
government organization. It could be the Great Barrier Reef, the town in which we live, or
even one of us.
Our description might take any form, such as drawings, plans or photographs, but let
us assume that it is a narrative written in English. That narrative might include many
statements that are merely opinions, so we will try to restrict ourselves to ones that we
collectively believe to be true.

Introduction

There will be two kinds of statements that we want to make.
1. Some will be simple facts, ones that make connections between specific objects; should
we decide to represent these kinds of facts in a computer system they will be stored in
a database of some kind.
2. Other facts will make more general statements about the nature of the organization;
these tend to end up in computer programs.

Specific Statements
The vast majority of the things that we might write down will be relatively simple statements
of fact. These will relate particular objects in some way. Some examples of such statements
might be as follows.

Bill Smith is a senior programmer.
In the December quarter, the Jones family used 1600 kilowatt hours of electricity.
F. Garcia owns the \'River Breezes\' property.
The Accounts Department is located at Head Office.
On Tuesday, 31 March, Ann Hampson spent two hours on the Fingle project.
These facts relate specific things particular people, jobs, dates, quantities and locations,
for example. There may be billions of facts of this kind. They constitute the raw data or
database upon which all information systems are founded. As a consequence of these large
numbers:
1. The facts are often partitioned in order to be more manageable, and so we have a
Customer database, a Personnel database and so on.
2. Even then, a database may contain millions of facts. Yet a typical transaction might
involve only two or three of these facts. Complex access methods are involved in
enabling rapid access to the required information.
But it is considerations of technology and volume that drive these facts into a database to be
controlled by a database management system, not anything intrinsic to the facts themselves.
It is technological considerations that force us to make the division between simple facts
and the more generalized ones.

General Statements
Of the things we might like to say, some will require more complex language, for example:
Senior programmers and above are not paid overtime.
A client may own several properties but a property is owned by only one client.
The quarterly tariff for the use of electricity is 15 cents per kilowatt hour (kWh) for the
first 300 kWh, 10 cents per kWh for the next 900 kWh, and 5 cents per kWh for the
remainder.
If two successive electricity meter readings are such that the second is less than the first,
then meter tickover is assumed to have occurred (that is, the meter has reached its limit
and reset itself).

What makes these statements more complex? Clearly they are longer, but they are longer
because they are trying to say more. They seem to be making more general statements
about classes rather than individuals; and in being more general, they are also more stable,
that is, they tend to remain true for a longer period. If this had not been the case, then
programming would have been quite a different discipline.

Let us call these more complex statements knowledge. Taken in conjunction with the
specific facts given previously, we can say, for example, that any claim for overtime made
by Bill Smith will be rejected, and that the Jones family will be charged $155 for their
electricity. How many statements of knowledge might be made regarding the organization
tens? thousands? tens of thousands? The answer is that there are probably millions. A
great many, but still several orders of magnitude fewer than the simpler facts that accompany
them.

Where do we store this knowledge? Do we have a knowledge base for complex facts,
one that mirrors the use of a database for simple facts? In practice, we usually bundle
together a number of them and encode them using the currently favored programming
language. So the organization\'s computer programs constitute its knowledge base.
Do we have a knowledge base management system (KBMS) to manipulate and modify
this knowledge? Most certainly not! Well we don\'t have a computerized KBMS, but
one of the major roles of the Computing Department in any organization is to act as a
knowledge base management system. One of that department\'s most important jobs is the
maintenance and enhancement of the organization\'s knowledge base. This is done through
the tasks of program maintenance and new systems development.

The knowledge base represents a kind of theory of that company. It represents the way
that the company believes that it works and how it interacts with its environment. However,
it is a theory that is being constantly revised and refined, as the organization adjusts to that
environment.