UML Weekend Crash Course™ - To Parent Directory

SESSION
23
Applying the Extended Statechart
Features to the Case Study
Session Checklist
✔ Deriving a Statechart diagram from a Sequence diagram
✔ Building a Statechart diagram for the case study
Those who use the UML diagrams often miss the benefit of building and comparing the
different diagrams. Each diagram provides a unique view of the same problem.
Comparing and contrasting these views can function much like reconciling your checkbook.
Given multiple sources of the same information, it is much easier to find and correct
errors.
Deriving a Statechart from Sequence Diagrams
The dynamic model provides two diagrams that model changes over time: the Statechart diagram
and the Sequence diagram. The key to understanding the relationship between these
diagrams is in understanding states and events. Events trigger transitions between states.
States capture the condition of an object during the period of time between transitions.
Using this understanding, look at the Sequence diagram shown in Figure 23-1.
In Figure 23-1, each vertical column represents the lifeline for one object. Each event
directed at a lifeline represents an event that may trigger a change in that object. The space
between events on the lifeline represents a period of time when the object remains in the
same condition or state. Because not every event causes a state transition, these periods are
referred to as candidate states until it’s proven that a change, in fact, occurs.
The events pointing outward from the object lifeline represent either return values sent
to other objects or send events.