In a sequence diagram, what does a lifeline represent?
Think about what entities are shown interacting in the diagram.
A lifeline represents an object or participant in the system that takes part in the interaction. It is shown as a vertical dashed line.
Which type of message in a sequence diagram indicates a synchronous call where the sender waits for the receiver to finish?
Consider which message type requires the sender to wait for a response.
A synchronous message is a call where the sender waits for the receiver to complete processing before continuing.
What does an activation bar (also called execution specification) represent on a lifeline in a sequence diagram?
Think about what shows when an object is busy doing something.
An activation bar is a thin rectangle on a lifeline that shows when an object is active and executing a process.
Which of the following best describes the difference between synchronous and asynchronous messages in sequence diagrams?
Consider the sender's behavior after sending the message.
Synchronous messages require the sender to wait for the receiver to finish processing, while asynchronous messages allow the sender to continue immediately.
Consider a sequence diagram with three lifelines: User, Controller, and Database. The User sends a synchronous message to Controller, which then sends two asynchronous messages to Database. The Database replies with two return messages to Controller, and Controller sends a return message back to User.
How many messages are shown in total in this sequence diagram?
Count all messages including calls and returns.
Messages are: 1 synchronous call (User to Controller), 2 asynchronous calls (Controller to Database), 2 return messages (Database to Controller), and 1 return message (Controller to User), totaling 6 messages.