When designing an event-driven system, it is crucial to correctly define event types based on their role and impact. Properly categorizing events ensures system efficiency, maintainability, and scalability. Below, we explore the primary event types, their characteristics, and practical use cases.

1. Domain Events

Domain Events represent significant business process changes that occur within a system. These events capture important business logic executions and data modifications.

• Reflects key business milestones and state transitions.
• Often used in Event Sourcing and CQRS architectures.
• Helps maintain business consistency across microservices.

Examples: OrderPlaced, UserRegistered, PaymentConfirmed.

2. Integration Events

Integration Events enable inter-service communication in distributed architectures. They ensure reliable message passing and data synchronization between microservices.

• Promotes loose coupling between services.
• Works asynchronously via event-driven messaging systems.
• Ensures eventual consistency across service boundaries.

Examples: OrderShipped, InventoryAdjusted, UserProfileUpdated.

3. Notification Events

Notification Events are designed for real-time updates, logging, or alerting. They primarily serve UI updates, logging mechanisms, and external notifications.

• Triggers user notifications and system alerts.
• Commonly used for analytics and monitoring purposes.
• Does not impact business logic directly.

Examples: EmailSent, SMSDelivered, UserLoggedIn.

4. Streaming Events

Streaming Events handle continuous data flows and real-time event processing. They are widely used in telemetry, monitoring, and user behavior tracking.

• Designed for high-frequency data transmission.
• Essential for IoT systems, stock trading platforms, and analytics pipelines.
• Often processed using stream processing frameworks like Kafka Streams or Apache Flink.

Examples: SensorDataReceived, ClickStreamEvent, MarketPriceUpdated.