Skip to main content

Start event

A Start Event is a BPMN flow element that marks the point where a process or subprocess begins execution. It indicates when and under what conditions a process instance is created.

Key characteristics​

  • Creates a new process instance: A Start Event signals the initiation of a process. Each trigger results in one new instance.

  • No incoming sequence flows: By definition, it cannot have incoming connections, because nothing precedes the start.

  • Exactly one required in a top-level process: A process must have at least one Start Event. Subprocesses may have multiple start events (for event subprocesses).

  • Type of trigger determines activation: Depending on the type, Start Events react to specific triggers and create new process instances when those triggers occur:

    • None (manual start): The simplest start event — a process instance is created manually (via user action or API) without an external event.

    • Message: Starts a process when a message is received. Useful for integrating with external systems and event-driven architectures.

    • Timer: Starts instances based on time: at a specific date/time, after a duration, or on a repeating schedule (cron-based schedule).

    • Error (event subprocess): Used within event subprocesses to start a subprocess in response to an error condition thrown inside the same scope.

    • Signal: Starts instances in response to a broadcast signal. Signals are global (within the engine/cluster) and can start multiple process instances that listen for the same signal.

    • Escalation: Starts an event subprocess when an escalation is raised. Typically used to escalate issues to higher-level part of the process.

    • Conditional: Starts a process when a specified condition evaluates to true (based on process variables or external state). Useful for reactive or rule-based instantiation.

    • Compensation: Starts compensation handlers for previously completed activities when compensation is triggered for the scope.

    • Multiple triggers: A Start Event can be modeled with multiple event definitions (or a process can have multiple Start Events). Each defined trigger can independently create instances when its condition is met.

    Allowed contexts

    • Allowed in main process:

      • None
      • Message
      • Timer
      • Conditional
      • Signal

    • Allowed only in Event Subprocess:

      • Error
      • Escalation
      • Compensation

Graphical notation​

Start event usage example

A thin single-line circle.

XML Definition​

<bpmn:startEvent id="startEvent" name="Start">
  <bpmn:outgoing>MyFlow</bpmn:outgoing>
</bpmn:startEvent>

Current Implementation​

Start event is fully supported.