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How to understand the UML sequence diagram, in view of this problem, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible method.

Brief introduction of UML sequence Chart

A timing diagram (SequenceDiagram) is an interaction diagram that emphasizes the timing of messages. A timing diagram describes the interactions between classes in a class system, and it models these interactions as message exchanges. A timing diagram is a model that describes how groups of objects collaborate on certain behaviors over time.

A timing diagram is an interaction diagram that emphasizes the timing of messages. It consists of Actor, Object, Message, Lifeline and Focusofcontrol. In UML, an object is represented as a rectangle with an underscore in its name, a message is represented by a marked arrow in a timing diagram, a lifeline is represented by a dotted line, and the control focus is represented by a thin rectangle.

The time series diagram represents the interaction as a two-dimensional graph, which is vertically the time axis, and the time extends downward along the vertical line. The horizontal axis represents the meta-roles of individual objects in collaboration. The activities of meta-roles are represented by lifelines. When the object exists, the lifeline is represented by a dotted vertical line, and when the process of the object is active, the lifeline is a dual channel. Messages are represented by arrows from one object's lifeline to another, and the arrows are arranged from top to bottom in the diagram in chronological order.

General criteria for designing UML sequence diagrams

Try to keep the messages in order from left to right

Layer the classifier

Avoid modeling object Destruction

Principles of classifier

The principle of message

Create objects directly

Specify the type for the parameter placeholder

Class is implemented as a static operation

The principle of return value

Do not model the return value when the return value is obvious. The return value is displayed using a dotted arrow marked with the return value, and the return value is optional.

Indicate the type of the return value placeholder

Clearly indicate the actual value for a simple value

The use of UML sequence diagrams

Describe the overall sequence of control flows when there are multiple short methods between different classes.

Displays concurrent processes and activation.

Displays time series that are difficult to describe in the collaboration diagram.

Displays general forms that involve class interaction but have nothing to do with objects.

The dynamic model describes the behavior of the system over time, which is described by the change of the instantaneous value of the system extracted from the static view. In the performance of UML, the dynamic model is mainly to establish the interaction diagram and behavior diagram of the system.

Interaction diagrams include sequence diagrams and collaboration diagrams, while behavior diagrams include state diagrams and activity diagrams.

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.

Elements of UML sequence diagrams

The timing diagram includes the following elements: class roles, lifelines, activation periods, and messages

1, ClassRole

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

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 sequence diagram perform an operation, and the narrow rectangle on each lifeline in the sequence diagram represents the active period. It can be understood as a pair of curly braces "{}" in the semantics of C language.

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

The answer to the question on how to understand the UML sequence diagram is shared here. I hope the above content can be of some help to you. If you still have a lot of doubts to be solved, you can follow the industry information channel to learn more about it.

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