Mastering BPMN Event Notation: A Comprehensive Guide with Examples

Business Process Model and Notation (BPMN) is a standardized graphical notation for modeling business processes. BPMN events are a crucial part of this notation, representing occurrences that happen during the course of a process. This guide provides a detailed overview of BPMN event notation, including many examples.

BPMN Events: A Structured Overview
Events in BPMN (Business Process Model and Notation) are represented by circles and signify occurrences that impact a process. They define how a process responds to internal or external triggers, with the trigger type indicated by an icon inside the circle. Below is a detailed breakdown of BPMN events, their types, and usage:

Key Characteristics of BPMN Events

1. Event-Triggered Behavior
   • Events initiate actions based on specific triggers (e.g., a message, timer, or error).
2. Hierarchy of Events
   • Level 1: Basic events (None, Message, Timer start events; None, Message, Terminate end events).
   • Level 2: Expanded events (Intermediate events, Error, Escalation, Conditional, Signal, Link).
3. Visual Indicators
   • Intermediate Events: Double-ring circles.
   • Boundary Events: Attached to activities to handle exceptions or parallel actions.

Event Types and Their Functions

1. Start Events

Indicate where a process begins.

• None Start Event
  • Trigger: None (unspecified or manual start).
  • Use Case: Subprocesses (mandatory) or top-level processes with undefined triggers.
• Message Start Event (✉️)
  • Trigger: External message.
  • Use Case: Process starts when a message is received (e.g., customer request).
• Timer Start Event (⏰)
  • Trigger: Scheduled time/date.
  • Use Case: Recurring processes (e.g., monthly report generation).
• Multiple Start Event
  • Trigger: Any one of multiple triggers.
  • Use Case: Processes with flexible initiation points.

2. End Events

Indicate where a process concludes.

• None End Event
  • Result: No signal emitted.
  • Use Case: Default process completion.
• Message End Event (✉️)
  • Result: Sends a message upon completion.
  • Use Case: Notify external systems/users (e.g., order confirmation).
• Terminate End Event (⛔)
  • Result: Aborts all parallel flows.
  • Use Case: Handle critical exceptions (e.g., system failure).

3. Intermediate Events

Occur between start and end events.

• Catching Timer Event (⏰)
  • Action: Delays the process until a specified time/duration.
  • Use Case: Wait for a deadline (e.g., payment window).
• Throwing Message Event (✉️)
  • Action: Sends a message and continues the flow.
  • Use Case: Equivalent to a “Send Task” (e.g., notify a supplier).

4. Boundary Events

Attached to activities to handle exceptions or parallel actions.

• Interrupting Boundary Event
  • Behavior: Stops the activity and triggers an exception flow.
  • Use Case: Error handling (e.g., payment failure).
• Non-Interrupting Boundary Event
  • Behavior: Runs parallel to the activity.
  • Use Case: Monitoring (e.g., progress reminders during a task).
• Boundary Timer Event (⏰)
  • Action: Triggers if the activity exceeds a time limit.
  • Use Case: SLA enforcement (e.g., escalate overdue tasks).

Specialized Event Types

• Error Event (❌)
  • Use Case: Interrupting exceptions (e.g., system crash).
• Escalation Event (📈)
  • Use Case: Non-interrupting exceptions (e.g., manager approval required).
• Signal Event (⚡)
  • Behavior: Broadcasts a signal to all listening processes.
  • Use Case: Cross-process coordination (e.g., system-wide alerts).
• Link Event (🔗)
  • Behavior: Connects two sections of a process.
  • Use Case: Simplify complex diagrams (e.g., paginated workflows).

Key Considerations

1. Message vs. Signal
   • Message: Directed to a specific process/instance.
   • Signal: Broadcast to all processes (no specific target).
2. Event Subprocesses
   • Introduced in BPMN 2.0 to handle exceptions or recurring actions (e.g., logging errors).
3. Error vs. Escalation
   • Use Error for interrupting exceptions; Escalation for non-interrupting ones.

Best Practices

• Use Timer Start Events for scheduled processes to clarify instance meaning.
• Avoid overusing Terminate End Events; reserve them for critical exceptions.
• Prefer Non-Interrupting Boundary Events for monitoring to avoid disrupting workflows.

By mastering these event types and their triggers, modelers can create precise, efficient BPMN diagrams that reflect real-world process behavior.