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This article will explain in detail what elements are in the UML sequence diagram. The editor thinks it is very practical, so I share it for you as a reference. I hope you can get something after reading this article.

UML sequence diagram

Time sequence diagrams (SequenceDiagram) are used to show the relationship between objects, emphasize the chronological order of messages between objects, and show the interaction between objects.

The UML sequence diagram includes the following elements, class roles, lifelines, activation periods, and messages.

1. Class role (ClassRole)

The class role represents the role played by the objects in the UML sequence diagram in the interaction, at the top of the sequence diagram. Class roles generally represent the actual object.

2. Lifeline (Lifeline)

The lifeline represents the existence of the objects in the sequence diagram over a period of time. There is a vertical dotted line between each object and the center of the bottom in the timing diagram, which is the lifeline of the object, and the messages between objects exist between the two dotted lines.

3. Activation period (Activation)

The activation period represents the period during which objects in the uml sequence diagram perform an operation, and the narrow rectangle on each lifeline in the sequence diagram represents the active period.

4. Message (Message)

Messages are classes that define the exchange of information in interaction and collaboration, which are used to model the content of communication between entities, and information is used to transfer information between entities. Allows entities to request other services, and class roles communicate by sending and receiving information.

UML sequence diagrams describe how objects interact and focus on message sequences. That is, describe how messages are sent and received between objects. The time series diagram has two axes: the ordinate axis shows the time, and the Abscissa axis shows the object. Each object is represented by an object or class name written in a rectangular box with an underscore under the name, and a vertical dotted line indicating the execution of the object in the sequence (that is, the activity of the message object sent and received). This dotted line is called the lifeline of the object. Communication between objects is represented by horizontal message lines between the lifelines of objects, whose arrows indicate the type of message, such as synchronous, asynchronous, or simple. The way to browse the sequence diagram is to look at the messages exchanged between objects from top to bottom and analyze the message exchanges that occur over time.

The messages in the UML sequence diagram can be signals, operation calls, or similar to RPC (RemoteProcedureCall, remote procedure call) in C++ or RMI (RemoteMethodInvocation, remote method call) in Java. When an object receives a message, an activity in the object starts, a process we call Activation. Activation displays the control focus, indicating that the object starts execution at a certain point in time. An activated object either executes its own code or waits for another object to return (the activated object has sent a message to another object). On the graph, activate the drawing as a thin, tall rectangle on the lifeline of the object.

Messages can be identified by message names and parameters. The message can also have a conditional expression that branches or decides whether to send the message. If used to represent branches, each branch is mutually exclusive, that is, only one message in the branch can be sent at a time. Messages can also have sequence numbers, but in a sequence diagram, the sequence number of a message is rarely used because the sequence diagram already explicitly represents the order of the message.

This is the end of the article on "what are the elements of the UML sequence diagram". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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