Modeling is an activity that has been carried out over the years in software development. When writing applications by using the simplest languages to the most powerful and complex languages, you still need to model. Modeling can be as straightforward as drawing a flowchart listing the steps carried out by an application. Why do we use modeling? Defining a model makes it easier to break up a complex application or a huge system into simple, discrete pieces that can be individually studied. We can focus more easily on the smaller parts of a system and then understand the "big picture." Hence, the reasons behind modeling can be summed up in two words:

* Readability

* Reusability

Readability brings clarity—ease of understanding. Understanding a system is the first step in either building or enhancing a system. This involves knowing what a system is made up of, how it behaves, and so forth. Modeling a system ensures that it becomes readable and, most importantly, easy to document. Depicting a system to make it readable involves capturing the structure of a system and the behavior of the system.

Reusability is the byproduct of making a system readable. After a system has been modeled to make it easy to understand, we tend to identify similarities or redundancy, be they in terms of functionality, features, or structure.

Even though there are many techniques