Chapter 1. Introduction

The Unified Modeling Language (UML) is the standard modeling language for software and systems development. This statement alone is a pretty conclusive argument for making UML part of your software repertoire, however it leaves some questions unanswered. Why is UML unified? What can be modeled? How is UML a language? And, probably most importantly, why should you care?

Systems design on any reasonably large scale is difficult. Anything from a simple desktop application to a full multi-tier enterprise scale system can be made up of hundredsand potentially thousandsof software and hardware components. How do you (and your team) keep track of which components are needed, what their jobs are, and how they meet your customers' requirements? Furthermore, how do you share your design with your colleagues to ensure the pieces work together? There are just too many details that can be misinterpreted or forgotten when developing a complex system without some help. This is where modelingand of course UMLcomes in.

In systems design, you model for one important reason: to manage complexity. Modeling helps you see the forest for the trees, allowing you to focus on, capture, document, and communicate the important aspects of your system's design.

A model is an abstraction of the real thing. When you model a system, you abstract away any details that are irrelevant or potentially confusing. Your model is a simplification of the real system, so it allows the design and viability of a system to be understood, evaluated, and criticized quicker than if you had to dig through the actual system itself. Even better, with a formal modeling language, the language is abstract yet just as precise as a programming language. This precision allows a language to be machine-readable, so it can be interpreted, executed, and transformed between systems.

To effectively model a system, you need one very important thing: a language with which the model can be described. And here's where UML comes in.