Communicating flow with sequence diagrams

Sequence diagrams are another popular UML diagram. Sequence diagrams show a top-to-bottom flow of events as various systems and components interact to carry out a task.

Let’s add a Mermaid code cell to define a request from a client (such as a browser or desktop app) to a server and its underlying database:

sequenceDiagram
    Client->>Server: Request Data
    Server->>Database: SQL Query
    Database-->>Server: Query Results
    Server-->>Client: JSON Data

This syntax may not be exactly like others, but it should be familiar by this point in the chapter.

Notice how ->> syntax indicates a request and -->> indicates a response. This syntax governs whether the dotted line is shown on the relationship as illustrated in Figure 13.14:

Figure 13.14 – A sequence diagram

Our sequence...