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This article mainly introduces the overview and composition of UML sequence diagrams. In daily operation, I believe many people have doubts about the overview and composition of UML sequence diagrams. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts about the overview and composition of UML sequence diagrams. Next, please follow the editor to study!

UML sequence diagram

1. Overview

The UML sequence diagram (SequenceDiagram) describes the chronological order in which messages are sent between objects, which is used to represent the order of actions in the use case.

The timing diagram contains four elements: object (Objce), lifeline (Lifeline), message (Message) and Activation (activation).

The UML sequence diagram is represented as a two-dimensional diagram. The vertical axis is the time axis, and time extends downward along the vertical line. The horizontal axis represents individual objects in collaboration. When the object exists, the lifeline is represented by a dotted line, and when the process of the object is active, the lifeline is a double-track line. The arrow representation of a message from one object's lifeline to another object's lifeline.

The composition of 2.UML sequence diagram

1. Object

The object symbols in the sequence diagram are the same as those used in the object diagram, using a rectangle to contain the object name, and the object name is underlined. Placing the object at the top of the timing diagram means that the object already exists at the beginning of the interaction, and if the object is not at the top, it means that the object is created in the course of the interaction.

2. Lifeline

The lifeline represents the existence of objects in the UML sequence diagram over a period of time. It's a vertical dotted line.

3. Message

A message defines some form of communication between objects, which is an one-way communication between objects. Messages can be used to pass parameters between objects, either as signals or as calls.

Common message symbols in UML sequence diagrams are as follows:

The party indicated by the message arrow is the recipient.

4. Activate

UML sequence diagrams can describe the Activation and Deactivation states of objects. Activation means that the object is occupied to complete a task, and deactivation means that the object is idle and waiting for a message. The active state in UML is represented as a rectangle.

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