**System**

The complex interaction between diverse components is called as System.

**System Variables**

A state variable is one of the set of variables that are used to describe the mathematical “state” of a dynamical system. State variables are used to represent the states of a general system. example: In electrical circuits, the node voltages and the currents through components are usually the state variables.

**Model**

While designing /analysing a system, we require some concept of how its variables relate to each other, such a relationship between observed signals of the system is called as model of a system.

Models of a system may be defined in various ways and varying degree of mathematical complexity. The intended use of the model will determine the degree of satisfaction i.e. required to make the model useful.

**Identification**

The experimental modelling of a mathematical relationship is called identification.

Pure Identification =

**Black box modelling**
Pure Mathematics =

**White box modelling**
Combination of Identification and Mathematics =

**Grey Box modelling**

**Types of Model**

1. Experimental Based Model

2. Graphical Model

3. Mathematical Model

4. Software Program