UML Weekend Crash Course™ - To Parent Directory

Answers to Part Reviews 325
Sunday Morning Review Answers
1. When all the actions associated with the transitions into a state are the same, you
can model them as a single entry action. Place the description of the action you
want the object to perform whenever it enters the state in the internal transition
compartment of the state.
2. When all the actions associated with the transitions out of a state are the same,
you can model them as a single exit action. Place the description of the action you
want the object to perform whenever it leaves the state in the internal transition
compartment of the state.
3. If an outgoing transition is added that does not require the action, you cannot use
the exit action. An exit action means that the action will always be performed
when the object exits that state.
4. In front of the action expression put the object name; separate the name from the
action with a period. This is often called dot notation.
5. Activities. Activities may be interrupted because they do not alter the state of the
object.
6. A call event is the most common event type. It is basically the invocation of an
operation on the receiving object.
7. A time event evaluates the passage of time as a trigger. It implies that the object
supports some mechanism to monitor the passage of time. Use the keyword after
to specify the time increment to be evaluated.
8. A guard condition controls the response to an event. When an event occurs, the
condition is tested. If the condition tests true, the corresponding transition takes
place along with any and all associated actions; otherwise the event is abandoned.
9. A change event tests for a change in the object or a point in time. Use the keyword
when with the required test.
10. A substate is a state within a state, a lower level of detail within a state. The
substates are placed within the expanded superstate.
11. The state of an object expresses its current condition. The condition is reflected in
the values of the attributes of the object. A change in the attribute values that
define the state redefines the state of the object.
12. A Sequence diagram models a timeline for each object. It also models events
that affect the object. The spaces on the timeline between those events represent
periods of time when the condition of the object does not change. These periods of
time, the gaps on the timeline, represent candidate states.
13. Typically, only the events pointing at the object’s timeline affect a change in the
object. The outgoing arrows represent messages to other objects. (Sending a message
usually does not change a state unless it causes a wait state until the reply
arrives.)
14. A state describes an object. An object is usually named with some form of noun.
Words that describe nouns are called adjectives. So the object Order may be
described as a Placed Order, a Filled Order, or a Cancelled Order.