UML Distilled: A Brief Guide to the Standard Object Modeling Language, Second Edition

Generalization

A typical example of generalization involves the personal and corporate customers of a business. They have differences but also many similarities. The similarities can be placed in a general Customer class (the supertype), with Personal Customer and Corporate Customer as subtypes.

This phenomenon is also subject to different interpretations at the different levels of modeling. Conceptually, we can say that Corporate Customer is a subtype of Customer if all instances of Corporate Customer are also, by definition, instances of Customer. A Corporate Customer is then a special kind of Customer. The key idea is that everything we say about a Customer—associations, attributes, operations—is true also for a Corporate Customer.

Within ...