Introduction to Event Storming

Event Storming is a collaborative modeling technique that helps teams explore complex business domains. It was introduced by Alberto Brandolini and has become a valuable tool in Domain-Driven Design (DDD) and Event-Driven Architecture (EDA).

Why Event Storming?

At FlowMart, we use Event Storming because it:

• Brings together domain experts and technical teams
• Helps identify domain events, commands, and aggregates
• Aligns perfectly with our event-driven architecture
• Facilitates better understanding of business processes
• Helps in defining service boundaries and responsibilities

Example Event Storming Session

Here is an example of an event storming session for the Orders domain.

Key Concepts

Domain Events

• Represent something significant that has happened in the business domain
• Written in past tense (e.g., “Order Placed”, “Payment Received”)
• Captured on orange sticky notes during the session

Commands

• Triggers that cause domain events
• Written in imperative form (e.g., “Place Order”, “Process Payment”)
• Captured on blue sticky notes

Aggregates

• Business entities that ensure consistency
• Group related events and commands
• Captured on yellow sticky notes

Policies

• Business rules that react to events
• Automated processes or human workflows
• Captured on purple sticky notes

Event Storming Levels

1. Big Picture Event Storming

   • High-level view of the entire business domain
   • Focuses on major events and workflows
   • Helps identify bounded contexts

2. Process Level Event Storming

   • Detailed view of specific processes
   • Includes commands, policies, and external systems
   • Helps design individual services

3. Software Design Level Event Storming

   • Technical perspective of the domain
   • Includes aggregates, entities, and value objects
   • Leads to implementation decisions

Benefits for FlowMart

Event Storming has helped us:

• Design our microservices architecture
• Identify service boundaries
• Define event contracts between services
• Improve collaboration between teams
• Reduce misunderstandings and rework

Prerequisites for Event Storming

To conduct an effective Event Storming session, you’ll need:

• A large modeling space (physical or virtual)
• Sticky notes in different colors
• Domain experts and technical team members
• A skilled facilitator
• 2-4 hours of uninterrupted time

Next Steps

Continue reading to learn:

• How to Facilitate an Event Storming Session
• From Event Storming to Implementation