Event Storming

Event Storming Rules

1. Overview

Event Storming is a workshop-based technique created by Alberto Brandolini for collaboratively exploring complex business domains using sticky notes on a wide modeling surface.

Goals

• Build shared understanding of the business domain across all stakeholders
• Break silos between departments (business, development, design)
• Discover domain events, processes, pain points, and boundaries
• Transition workshop results into software architecture (DDD)

Participants

• Domain experts (business stakeholders) — essential
• Developers and architects
• UX designers, product managers
• Ideal size: 6-8 people (Big Picture can handle 10-20+)

2. Sticky Note Color Conventions

Visual Flow (Design Level)

[Actor] → [Command] → [Aggregate] → [Domain Event] → [Policy] → [Command] ...
              ↑                                            ↓
         [Read Model]                              [External System]

                         [Hot Spot]

3. Workshop Levels

Big Picture

Goal: Macro-level understanding of the entire business domain.

Agenda:

1. Introduction and goal alignment (10-15 min)
2. Optional warm-up with familiar process (20 min)
3. Chaotic exploration — freely generate domain events (25 min)
4. Enforce timeline — arrange events chronologically (30-45 min)
5. Mark Hot Spots — questions, conflicts, unknowns (15-20 min)
6. Add External Systems and Actors
7. Draw Bounded Context boundaries
8. Wrap-up and agree on next steps (30 min)

Process Modeling

Goal: Detailed design of a specific business process.

Design Level

Goal: Detailed model translatable 1:1 into code.

Steps:

1. Set goal for the session
2. Identify Domain Events
3. Add Commands
4. Determine Actors and Policies
5. Place empty Read Model stickies
6. Sketch Read Model / UX mockups
7. Map External Systems
8. Place empty Business Rule stickies (Blank Aggregates technique)
9. Write business rules (invariants, pre/post conditions)
10. Group business rules by Aggregate
11. Name each Aggregate

For the detailed facilitation guide, see references/facilitation-guide.md.

4. Facilitation Techniques

Preparation

• Modeling space: Minimum 1m × 10m paper roll or wide wall
• Materials: Colored sticky notes (7.6cm × 7.6cm, super-sticky), fine markers (0.8mm), masking tape
• No chairs: "Seats are poisonous" — standing maximizes engagement
• Clear goal: Define what the workshop should achieve before starting

Time Management

• Set timers for each phase (can extend, but limits maintain flow)
• Alternate 10-15 min silent ideation with facilitator-led merging
• Reserve the last 30 minutes for Hot Spot review and action items

Engagement

• Ask open questions, allow silence (invite, don't force participation)
• Approach quiet participants individually to re-explain instructions
• Create urgency: "We'll review in 10 minutes"
• If one person dominates, split the group to work on separate board sections

Quality Control

• Rotate low-quality stickies 45° to flag them for rewriting
• Record decisions on a separate flipchart for tracking
• Proactively expand modeling space before it runs out

Conflict Resolution

• Do not chase excessive consensus (prevents groupthink)
• Mark disagreements as Hot Spots (red stickies) and move on
• Resolve in dedicated follow-up sessions

5. Transition to DDD

Bounded Context Identification

• Event flow in Big Picture naturally reveals domain boundaries
• Use "Functional Area" instead of "Bounded Context" for accessibility
• Draw boundaries with solid lines after understanding forms (never prematurely)
• Name each context with a pink sticky

Aggregate Identification (Blank Aggregates Technique)

1. Do NOT ask participants to identify Aggregates directly
2. Place blank stickies and ask for business rules (invariants, constraints)
3. Let developers naturally group rules "as they would in code"
4. Grouped clusters become Aggregates — name them last

Next Steps After Workshop

• Start implementation using identified Aggregates and Events
• Use Example Mapping for deeper business rule analysis
• Draw a Context Map to define relationships between Bounded Contexts (Partnership, Customer-Supplier, Conformist, ACL, etc.)
• For DDD tactical patterns, see the ddd skill

6. Remote Event Storming

Recommended Tools

Remote Best Practices

• Short cycles: 10-15 min silent ideation → facilitator-led merge, repeat
• Verify access: Confirm board access for all participants before the session
• Cameras on: 90% of Event Storming is collaboration, 60% is non-verbal
• Dual screen: Facilitator uses one for the board, one for video chat
• Personal zones: Draw vertical lines to separate personal work area (left) from shared timeline (right)
• Co-facilitation: Use two facilitators for remote sessions
• Sign stickies: Participants initial their notes for accountability

7. Common Anti-Patterns