In software development it is common
to use the term inheritance rather than generalization . In Figure 3.18 , the
class Location inherits all properties from the class Waypoint . This means that an
object of type Location has an attribute coordinates in addition to the attribute
name . Not only attributes are inherited, but also constraints and operations, if
defined.
A generalization is denoted as an arrow with solid line and hollow triangle as
an arrowhead. It is read as ??? is a kind of ??? in the direction of the arrow. In Figure
3.18 , we read, ??? a location is a kind of waypoint. ???
The relationship forms a hierarchy. This is why we speak of superclasses and
subclasses. The class Location is a subclass of the superclass Waypoint .
A generalization is also permitted between actors and between use cases. It ??™ s
the same model element and the same concept in all cases. However, it must not
159 3.3 The Class Diagram
FIGURE 3-17
Example for an abstraction dependency.
pkg Models
Business process model
?«business process?»
Rental cars
System model on-board computer
Start car usage
?«trace?»
FIGURE 3-18
Example for a generalization.
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