UML Weekend Crash Course™ - To Parent Directory

Session 11—The Class Diagram: Aggregation and Generalization 125
Dog
Collie Spaniel Setter
Figure 11-7 Steps 1 and 2: Draw the starting superclass and the first set of specialized
classes (subclasses).
Step 2: Identify the discriminator for the first level of differentiation or specialization.
In this example I chose breed. List the possible values for the discriminator. Identify
what distinguishes the values from one another using the five objective criteria I
described earlier in “Elements of generalization.” Then create a class for each value.
In Figure 11-7, I broke Dog down into the breeds (discriminator) Collie, Spaniel, and
Setter.
Step 3: Connect all the Breed subclasses to the Dog superclass using the generalization
relationship, a line with the triangle at the superclass end of the line (see Figure
11-8). Place the discriminator label on the line. It doesn’t really matter where exactly,
as long as it is between the superclass and subclasses. Other analysts are going to
look at my diagram and wonder why I chose this set of subclasses. In any given
problem there might be quite a few different ways to organize the information.
Dog
Discriminator
Breed
Collie Spaniel Setter
Figure 11-8 Step 3: Draw the generalization relationship.
Step 4: The process continues by repeating the steps for each new subclass I create.
In Figure 11-9, I have expanded only the Spaniel subclass.