时序图 例图 UML

### UML Sequence Diagram Example

#### Course Creation Functionality

In the context of a course creation functionality, an illustrative sequence diagram can be constructed to demonstrate interactions between different objects involved in this process. The following elements are included:

- **Objects (Actors)**: These represent entities such as `User`, `CourseManager`, and `Database`.
- **Lifelines**: Vertical dashed lines that extend downward from each object symbolizing their existence over time.
- **Control Focuses**: Rectangles on lifelines indicating periods during which actions occur or messages are processed.
- **Messages**: Arrows connecting lifelines showing communication flow.

Below is a simplified version of how these components interact when creating a new course[^2]:

sequenceDiagram
    participant User
    participant CourseManager
    participant Database
    
    User->>CourseManager: Request create course(name="Math", description="Basics")
    activate CourseManager
    CourseManager->>Database: Insert(courseData={name:"Math",description:"Basics"})
    activate Database
    Database-->>CourseManager: Acknowledge insertion success
    deactivate Database
    CourseManager-->>User: Confirm course created successfully
    deactivate CourseManager

This example illustrates basic operations like sending requests, processing them through intermediary services (`CourseManager`), interacting with storage systems (`Database`), and finally confirming outcomes back to users.

For more complex scenarios involving loops or conditional branches within sequences, specific fragments may apply:

- For repetitive tasks, one might use loop constructs denoted by "loop". This could correspond to iterating over multiple items using structures similar to `for` or `foreach` statements found in programming languages[^3].

- Conditional logic can also be represented via alternative fragments marked as "alt", analogous to handling branching conditions seen in `if...then...else` expressions[^4].

By incorporating both simple message exchanges alongside advanced structural patterns, comprehensive models capturing various aspects of system behavior become possible.