Use Case and Swim Lane Diagrams
Definition
Two complementary ways to model process flow — the sequence of activities that carry a solution from beginning to end. Use cases describe interactions between actors and the system; swim lane diagrams are flow charts that add clear role/responsibility boundaries.
Core Ideas
Use cases
Describe interactions between actors (users, or even another system) and the system. They bring structure to requirements that would otherwise become an unordered list of “the system shall…”. A good use case lets you:
- get an overall sense of how the system works,
- show enough detail for end-to-end process flow,
- understand exceptions and how they’re handled,
- balance formality and informality.
Swim lanes
A flow chart annotated with actors, answering four questions:
- WHO — the actors/participants in the process
- WHAT — the step-by-step what happens (not how)
- WHEN — the flow direction (left→right or top→bottom)
- WHY — visually clear who does what and when
Good: well-spaced boxes, clear lines, all actors with their steps and hand-offs, focus on what. Bad: overlapping boxes, chaotic flow, detail of how, omitting minor actors.
Relationships
- Business Analysis — process modeling within requirements work
- User Stories — narrative requirements that use cases give structure to
- Event-Driven Architecture — process flows often map to event sequences