1 Introduction

Observation is the ultimate basis for our understanding of the world around us. But observation alone only gives information about particular events; it provides little help for dealing with new situations. Our ability and aptitude to recognize similarities and patterns in different events, to distil the important factors for a specific purpose, and to generalize our experience enables us to operate effectively in new environments. The result of this skill is knowledge, an essential resource for any intelligent agent.

Knowledge varies in sophistication from simple classification to understanding and comes in the form of principles and models. A principle is simply a general assertion and is expressed in a variety of ways ranging from saws, slogans, opinions to mathematical equations. They can vary in their validity and their precision. A model is, roughly speaking, an analogy or a mapping for a certain object, process, or phenomenon of interest. It is used to explain, to predict, or to control an event or a process. For example, a miniature replica of a car, placed in a wind tunnel, allows us to predict the air resistance or air eddy of a real car; a globe of the world allows us to estimate distances between locations; a graph consisting of nodes (corresponding to locations) and edges (corresponding to streets between the locations) enables us to find the shortest path between any two locations without actually driving between them; and a differential equation system enables us to balance an inverted pendulum by calculating at short intervals the speed and direction of the car on which the pendulum is fixed.

A model is a powerful means of structuring knowledge, of presenting information in an easily assimilated and concise form, of providing a convenient method for performing certain computations, of investigating and predicting new events. The ultimate goal is to make decisions, to control our environment, to predict events, or just to explain a phenomenon.

  1.1 Models and their Functions
  1.2 The Advent of the Computer
  1.3 New Scientific Branches Emerge
  1.4 The consequences