1. Determine the background of the interactive process;

2. Determine the interactive objects involved in the process;

3. Set a lifeline for each object;

4. Starting from the initial message, draw subsequent messages in turn;

5. Considering the nesting of messages and marking the time point when messages occur, FOC (control focus) is adopted;

6. Explain the location of the time limit.

1. Sequence diagram, also known as sequence diagram and sequence diagram, is a UML interaction diagram. It shows the dynamic cooperation between multiple objects by describing the time sequence of sending messages between objects. It can represent the behavior sequence of use cases. When a use case is executed, each message corresponds to a trigger event in the class operation or state machine, which leads to the transformation.

2. The sequence diagram describes how objects interact, with emphasis on the message sequence. That is, describe how messages are sent and received between objects.

The timing chart has two axes: the vertical axis represents time and the horizontal axis represents objects. The representation method of each object is: write the object and/or class name in a rectangular box, and underline the name; At the same time, there is a vertical dotted line that represents the execution of objects in the sequence (that is, the activities of sending and receiving message objects), which is called the lifeline of objects. The communication between objects is represented by a horizontal message line between object lifelines, and the arrow of the message line indicates the type of message, such as synchronous, asynchronous or simple.

3. The method of browsing the sequence diagram is to view the messages exchanged between objects from top to bottom and analyze the message exchanges that have occurred over time.