UML Weekend Crash Course™ - To Parent Directory

174
Saturday Afternoon
REVIEW
The dynamic view includes diagrams designed to illustrate how objects work together. The
Sequence and Collaboration diagrams specifically show how objects talk to one another to
accomplish a goal of the system, one scenario in a Use Case, or one operation.
The Sequence diagram is built around three fundamental elements: the objects, messages,
and the object lifeline. The objects represent the participants. The messages
represent the communication that they send to one another. The object lifelines
allow us to arrange the messages in the proper relative sequence.
Messages may be synchronous (requiring a response) or asynchronous (not requiring
a response). A simple or synchronous message uses a solid line with a solid arrowhead.
The asynchronous message uses a solid line with a stick arrowhead. Both of
these message types represent the invocation of an operation on the object they are
pointing to. So the name of the message becomes an operation signature with the
name, arguments, and return type.
The return from or answer to a message uses a dashed line and a line-style arrowhead.
The return is simply information, so it is written on the return arrow.
A message may be conditional on some prior result. This can be shown using the
guard condition notation placed in front of the operation name.
An object may be active or inactive at various times in the Sequence diagram. To
show that an object is busy, use a narrow vertical rectangle, called an activation bar,
on the object lifeline from the time the object becomes active to the time that it
stops. An object usually becomes active because it has been asked to do something.
It becomes inactive when it is finished with the current task.
When an object is deleted or destroyed, the timeline ends and an X marks the
termination.
QUIZ YOURSELF
1. What does the dynamic view represent (See “Knowing the purpose of Sequence
and Collaboration diagrams.”)
2. Where do you place the participating objects in a Sequence diagram (See
“Defining the basic notation of the Sequence diagram.”)
3. How does the Sequence diagram show that one object tells another object to do
something (See “Defining the basic notation of the Sequence diagram.”)
4. How does the Sequence diagram show that an object is busy (See “Defining the
extended notation for the Sequence diagram.”)
5. How does the Sequence diagram show that an object no longer exists (See
“Defining the extended notation for the Sequence diagram.”)