UML sequence diagram (timing diagram)

first, the definition:

Time series diagrams (Sequence Diagram), also known as sequence or sequential plots, are UML behavior diagrams.

It shows the dynamic collaboration between multiple objects by describing the chronological order in which messages are sent between objects. It can represent the sequence of behavior of a use case, and when a routine is performed, each message in a sequence diagram corresponds to a class operation or trigger event that causes a transition in the state machine.

second, time series diagram elements

The modeling elements included in the time series diagram are: Role (actor), Object, Lifeline (Lifeline), control focus (focus on control), message
A. Role (actor)
System roles, which can be people, and even other systems or subsystems.
B. Objects (object)
object represents the role of an object in a sequence diagram in interaction

Objects typically contain the following three naming methods: The first way contains the object name and the class name. The second way is to display only the class name without displaying the object name, which is an anonymous object. The third way to display only object names does not display the class name.
C. Lifeline (Lifeline)
A lifeline is represented in a sequence diagram as a dashed line extending downward from the object's icon, indicating when the object exists
D Control focus (focus on control)/activation period (Activation)
The control focus is the symbol representing the time period in the time series, during which the object will perform the appropriate action. Represented by a small rectangle
E. Messages (message)
Messages are generally divided into synchronous messages (synchronous message), asynchronous messages (asynchronous msg)
and return messages (return message), self-correlating messages (Self-message)

Message type:
Synchronization messages (Synchronous message)
The sender of the message passes control to the recipient of the message, and then stops the activity, waiting for the recipient of the message to discard or return control. Used to indicate the meaning of synchronization. The sync message is a solid arrow;
Asynchronous messages (asynchronous message)
The message sender passes the message to the recipient of the message, and then resumes its activity without waiting for the recipient to return the message or control. The recipient and sender of an asynchronous message are working concurrently. An asynchronous message is a half-arrow;
Return message
Returns a message that represents a return from a procedure call
Self-correlating message (self-message)
Represents the method's own invocation and one method within an object that calls another method.

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