UML commonly used diagrams

1: Use case diagram

【Concept】Describe user needs, describe the function of the system from the user's point of view

[Description method] The ellipse represents a use case; the human-shaped symbol represents the role

[Objective] To help the development team to understand the functional requirements of the system in a visual way

【Use case diagram】

2: Activity diagram

[Concept] Describe the activities to be performed to meet the requirements of the use case and the constraints of the activity time

【Description method】 

1. Starting point: filled circle 
2. Activity: Rounded Rectangle 
3. End point: a circle containing a solid circle inside 
4. Swimlane: The object that actually performs the activity

[Purpose] Represents the process control flow between two or more objects when processing an activity

【Activity map】 

3: Interaction diagram

Used to describe the interaction between objects 

1. Sequence Diagram (Sequence Diagram)

[Concept] Describe the interaction sequence between objects, emphasizing the time sequence of message passing between objects

[Description method] Across the top of the figure, each box represents an instance or object of each class; the class instance name and class name are separated by colons

[Purpose] To display the calling relationship between different objects in the process, and also display different calls of different objects.

【Sequence Diagram】