Combined fragments gallery

Scenario

This is a compact tour of UML sequence constructs that matter in real service diagrams. The request validates auth, checks idempotency, retries a reservation, publishes asynchronously, persists state, and returns a response.

Annotation key

• alt, opt, loop, par, and critical are first-class combined fragments.
• ref over API, Auth references a reusable interaction instead of inlining it.
• ->> distinguishes asynchronous event publication from blocking calls.