UML Weekend Crash Course™ - To Parent Directory

210
Saturday Evening
Defining Internal Events and Activities
The state icon can also be expanded. The purpose of the expanded form is to reveal what
the object can do while it is in a given state. The notation simply splits the state icon into
two compartments: the name compartment and the internal transitions compartment, as
illustrated in Figure 20-12.
State name compartment
Internal transitions compartment
Figure 20-12 The expanded state icon
The internal transitions compartment contains information about actions and activities
specific to that state. You’ve seen actions associated with events. Here I’m talking about the
same actions, only documented as entry and exit actions within a state. But I’m going to
hold off until Session 21 to explain entry and exit actions so that I have room to explain
them with some illustrations. For now I want to focus on activities.
Activities are processes performed within a state. An activity tends not to be atomic, that
is, an activity may be a group of tasks. Activities may be interrupted because they do not
affect the state of the object. Contrast this with the earlier definition of an action, which
said that you must not interrupt actions because they alter the state. Stopping an action
midway could leave the object in an undefined state. Activities just do work. They do not
change the state of the object.
For example, Figure 20-13 models the active state of the Customer object. While in that
state, the customer object generates a monthly invoice for the customer’s purchasing activity
and generates monthly promotions tailored to the Customer. To model activities within a
state, use the keyword Do: followed by one or more activities.
Active
Do : generate monthly invoice
Do : generate monthly customer promotion
Figure 20-13 The expanded state icon with activities
These activities will be performed from the time the object enters the state until the
object leaves the state or the activity finishes.