UML diagrams

Five diagram types, each answering a different question about the same system. All five below build up the same running example - a login flow with a LoginForm, an AuthService and a Database - so you can compare what each diagram shows and what it deliberately leaves out.

• [Class diagram](./10. class-diagram.mdx) - the static shape: classes, their members, and how they relate.
• [Use case diagram](./20. use-case-diagram.mdx) - what an actor can do, from outside the system.
• [Sequence diagram](./30. sequence-diagram.mdx) - the order messages pass between objects, for one scenario.
• [Activity diagram](./40. activity-diagram.mdx) - a process, step by step, including its branches.
• [State machine diagram](./50. state-machine-diagram.mdx) - the states an object can be in and what triggers a move between them.