designing-event-modelslisted

# Designing Event Models ## Workflow: Design an Event Model 1. **Clarify scope.** Ask what system or feature to model. Identify actors, key business processes, and external systems. 2. **Brainstorm events.** List all domain events. Group into swimlanes by business capability. 3. **Build the timeline.** Order events chronologically within each swimlane. 4. **Apply the four patterns** to each step: - **State Change:** Screen → Command → Event - **State View:** Event(s) → Read Model → Screen - **Automation:** Event → Read Model → ⚙️ → Command → Event - **Translation:** External Event → ⚙️ → Command → Event 5. **Define slices.** Each pattern application = one slice. Name it after the business action or view. 6. **Write GWTs** (Given/When/Then scenarios) for each slice. Minimum: one happy path + one error/edge case. Use concrete example data ("Jane Doe", "$4.50"), never abstract placeholders. 7. **Run the Information Completeness Check.** For every field in every read model, trace it to a source event. For every command field, trace it to user input or a prior event. Flag gaps. 8. **Output the model as YAML** using the format below. ## Workflow: Review an Event Model 1. **Check completeness.** Every read model field must trace to a source event. Flag orphan data. 2. **Check anti-patterns:** - Events in present tense (should be past tense) - God slice (>10 GWTs in one slice — decompose) - Horizontal over-orchestration (UI firing sequential commands — use au