UML: Class Diagram (Essentials)

A class diagram describes the types of objects in the system and the various kinds of static relationships that exist among them. Class diagrams also show the properties and operations of a class and the constraints that apply to the way objects are connected.

The UML uses the term feature as a general term that covers properties and operations of a class.

The boxes in the diagram are classes, which are divided into three compartments: the name of the class (in bold), its attributes, and its operations. also shows two kinds of relationships between classes: associations and generalizations.

More specifically, each class has 3 fields: the class name at the top, the class attributes right below the name, the class operations/behaviors at the bottom.

Properties: represent structural features of a class. As a first approximation, you can think of properties as corresponding to fields in a class.

Attributes: the attribute notation describes a property as a line of text within the class box itself.

Associations: much of the same information that you can show on an attribute appears on an association. This is the same properties represented in the two different notations.