Lecture 1: introduction to modeling

What is Model?
The model is an abstraction of the system obtained by making a set of assumptions about how the system works. It must capture the essential characteristics of the system. The term ‘model’ is used in many different situations and in many different ways: “anything can be a model of anything” , “… every case of being taken as a model involves a restriction with respect to relevant properties" . A model of a system is anything an "experiment" can be applied to in order to answer questions about that system.
The Model is similar to but simpler than the system it represents. One purpose of a model is to enable the analyst to predict the effect of changes to the system. A model should be a close approximation to the real system and incorporate most of its features. It should not be so complex that it is impossible to understand and experiment with it.
The most important aims of the model are:
1. Model helps us to visualize a system as it is or as we want it to be.
2. Model permits us to specify the structure or behavior of system.
3. Model document the decision we have made.

What is System?
A system might be an object or collection of objects whose properties we want to study. It may be thought as a collection of elements which are interdependent and interact. It can be thought of as a collection of entities which are logically related and which are of interest to a particular application. A system can be almost anything. It can contain subsystems which are themselves systems. The following features of the system are of interest:
• Environment: Each system can be seen as a subsystem of a broader system.
• Interdependency: No activity takes place in total isolation.
• Sub-systems: Each system can be broken down to sub-systems.