Learning UML

The Object-Oriented Paradigm

Now that you know how to use simple UML words and sentences, let’s consider the object-oriented paradigm on which the UML’s semantics are based. We’ll look at how object-oriented concepts enable us to view the world around us, and at how the paradigm’s principles enable us to better manage change and complexity.

Concepts

The object-oriented paradigm is based on a few key concepts that enable us to view the world around us. The next few sections discuss these key concepts.

Classes, associations, objects, and links

Figures Figure 2-3 through Figure 2-5 represent general sentences, because they don’t identify particular projects, managers, teams, and so forth. The general concepts shown in the sentences are known as classes, and the general relationships are known as associations. Similar to natural languages, we can also communicate in the UML using specific sentences involving specific projects, managers, teams, and so forth, where specific concepts are known as objects and specific relationships are known as links.

A class defines a type of object and the characteristics of its objects, and an object is an instance of a class. For example, Figures Figure 2-4 and Figure 2-5 show three classes, including Manager, Team, and Project. We can have many managers, teams, and projects, and each specific manager, team, and project is an instance or object of its class. In the UML, a specific concept is shown using the same symbol as its general concept. ...