Events

Events represent something that happens during a process: a process starts, something is waited for, a result is emitted, an exception arises, time passes. Each event combines a position (start, end, intermediate catch, intermediate throw, boundary) with an event definition that says what kind of trigger or effect is involved.

Event definitions

The engine supports the following event definition types. Not every type is valid at every position.

Definition	XML element	Used for
None	(no event-definition child)	Plain start/end/throw points; the simplest form
Message	`messageEventDefinition messageRef="..."`	Send or wait for a correlated message
Timer	`timerEventDefinition` with `timeDate`, `timeDuration`, or `timeCycle` child	Schedule, wait, or fire on a cycle
Signal	`signalEventDefinition signalRef="..."`	Broadcast or wait for a named signal
Link	`linkEventDefinition name="..."`	In-process "goto" between throw and catch
Error	`errorEventDefinition errorRef="..."`	Throw or catch a business error
Escalation	`escalationEventDefinition escalationRef="..."`	Throw or catch an escalation up the scope hierarchy
Compensation	`compensateEventDefinition`	Trigger or handle compensation for completed activities
Conditional	`conditionalEventDefinition` with `condition` child	Fire when a FEEL expression turns `true`
Terminate	`terminateEventDefinition`	End the enclosing scope immediately

messageRef, signalRef, errorRef, and escalationRef must reference a top-level <message> / <signal> / <error> / <escalation> declaration in the same <definitions> block — see Global definitions.

Position × definition compatibility

	Start	End	Intermediate catch	Intermediate throw	Boundary
None	✓	✓	—	✓	—
Message	✓	✓	✓	✓	✓
Timer	✓	—	✓	—	✓
Signal	✓	—	✓	✓	✓
Link	—	—	✓	✓	—
Error	event sub-process only	✓	—	—	✓ (always interrupting)
Escalation	event sub-process only	✓	—	✓	✓
Compensation	event sub-process only	✓	—	✓	✓
Conditional	event sub-process only	—	—	—	✓
Terminate	—	✓	—	—	—

Start events

Start events define how a process or sub-process begins.

Attributes

Attribute	Default	Notes
`id`	—	Required
`name`	—	Optional
`isInterrupting`	`true`	Applies to start events inside event sub-processes only. Ignored on top-level start events.

Auto-start behavior

When a process is deployed, typed start events are registered so an instance is started automatically when the trigger arrives:

Definition	Trigger
None	Process started explicitly via API
Message	A message with the matching name is published
Signal	A signal with the matching name is broadcast
Timer	The configured time arrives. Recurring expressions (`R/PT1H`) re-arm after each firing; one-shot (date) expressions fire once and deactivate

Re-deploying the process under a new version deactivates the previous version's auto-start registrations and arms the new ones.

Examples

<!-- None start event -->
<bpmn:startEvent id="start">
  <bpmn:outgoing>f1</bpmn:outgoing>
</bpmn:startEvent>

<!-- Message start event -->
<bpmn:startEvent id="start-msg">
  <bpmn:outgoing>f1</bpmn:outgoing>
  <bpmn:messageEventDefinition messageRef="Msg_Payment" />
</bpmn:startEvent>

<!-- Recurring timer start (every hour) -->
<bpmn:startEvent id="start-timer">
  <bpmn:outgoing>f1</bpmn:outgoing>
  <bpmn:timerEventDefinition>
    <bpmn:timeCycle xsi:type="bpmn:tFormalExpression">R/PT1H</bpmn:timeCycle>
  </bpmn:timerEventDefinition>
</bpmn:startEvent>

<!-- Non-interrupting message start in an event sub-process -->
<bpmn:startEvent id="esp-start" isInterrupting="false">
  <bpmn:outgoing>f1</bpmn:outgoing>
  <bpmn:messageEventDefinition messageRef="Msg_Notify" />
</bpmn:startEvent>

Validation

Check	Severity
Executable process has no start event	Error
Start event has any incoming sequence flow (BPMN 2.0 §10.4.2)	Error
Error / escalation / compensation start event placed outside an event sub-process (BPMN 2.0 §10.4.2 — these triggers are only legal as the starter of an event sub-process)	Error
Conditional start event at top level — the engine does not auto-instantiate top-level conditional starts; use an event sub-process or external trigger	Warning
`messageRef` / `signalRef` / `errorRef` / `escalationRef` references an unknown definition	Error

End events

End events finish a path of execution. A process must have at least one reachable end event (or a node with no outgoing flow, which is treated as an implicit end).

Behavior by definition

Definition	Effect
None	Completes the path normally
Message	Publishes a message, then completes. With `quantum:taskDefinition` set, a worker performs the dispatch; otherwise the engine publishes directly
Error	Throws an error; propagates up the scope hierarchy to the nearest matching error boundary or error start event in an event sub-process
Escalation	Throws an escalation up the scope chain to the nearest matching listener. With `quantum:taskDefinition` a worker performs the dispatch
Terminate	Cancels the nearest enclosing activity scope (sub-process, ad-hoc sub-process, or root process) and continues from that scope's outgoing flow. At the root, the entire instance terminates. A terminate inside a called process ends only the called process
Compensation	Triggers compensation for completed activities in scope, or for the activity named by `activityRef`

Examples

<!-- None end event -->
<bpmn:endEvent id="end">
  <bpmn:incoming>f_last</bpmn:incoming>
</bpmn:endEvent>

<!-- Error end event -->
<bpmn:endEvent id="end-error">
  <bpmn:incoming>f_err</bpmn:incoming>
  <bpmn:errorEventDefinition errorRef="Err_Timeout" />
</bpmn:endEvent>

<!-- Terminate end event -->
<bpmn:endEvent id="end-terminate">
  <bpmn:incoming>f_abort</bpmn:incoming>
  <bpmn:terminateEventDefinition />
</bpmn:endEvent>

<!-- Message end event dispatched by a worker -->
<bpmn:endEvent id="end-msg">
  <bpmn:extensionElements>
    <quantum:taskDefinition type="send-notification" />
  </bpmn:extensionElements>
  <bpmn:incoming>f_notify</bpmn:incoming>
  <bpmn:messageEventDefinition messageRef="Msg_Done" />
</bpmn:endEvent>

Validation

Check	Severity
End event has any outgoing sequence flow (BPMN 2.0 §10.4.3)	Error
`messageRef` / `errorRef` / `escalationRef` references an unknown definition	Error
Message end event with no `messageRef` and no `quantum:taskDefinition`	Warning (publishes a nameless message)
Escalation end event with no `escalationRef` and no `quantum:taskDefinition`	Warning (throws a nameless escalation)

Intermediate catch events

Intermediate catch events pause the token until an external trigger arrives, then advance.

Behavior by definition

Definition	Behavior
Message	Waits for a correlated message matching the referenced name. If a buffered message is already available it fires immediately
Timer — `timeDuration`	Waits the specified ISO 8601 duration from the moment the event is reached
Timer — `timeDate`	Waits until the specified ISO 8601 datetime
Timer — `timeCycle`	Fires repeatedly on the cycle
Signal	Waits for a broadcast matching the referenced name; checks the buffer first
Link	Receives control from a matching link throw event of the same `name` in the same scope. Acts as a goto target

A catch event placed immediately after an event-based gateway must have exactly one incoming flow (from the gateway).

Examples

<!-- Message catch -->
<bpmn:intermediateCatchEvent id="catch-msg" name="Wait for Payment">
  <bpmn:incoming>f1</bpmn:incoming>
  <bpmn:outgoing>f2</bpmn:outgoing>
  <bpmn:messageEventDefinition messageRef="Msg_Payment" />
</bpmn:intermediateCatchEvent>

<!-- Timer catch (duration) -->
<bpmn:intermediateCatchEvent id="wait-5m" name="Wait 5 min">
  <bpmn:incoming>f1</bpmn:incoming>
  <bpmn:outgoing>f2</bpmn:outgoing>
  <bpmn:timerEventDefinition>
    <bpmn:timeDuration xsi:type="bpmn:tFormalExpression">PT5M</bpmn:timeDuration>
  </bpmn:timerEventDefinition>
</bpmn:intermediateCatchEvent>

<!-- Signal catch -->
<bpmn:intermediateCatchEvent id="catch-signal" name="Receive Abort">
  <bpmn:incoming>f1</bpmn:incoming>
  <bpmn:outgoing>f2</bpmn:outgoing>
  <bpmn:signalEventDefinition signalRef="Sig_Abort" />
</bpmn:intermediateCatchEvent>

<!-- Link catch (jump target) -->
<bpmn:intermediateCatchEvent id="catch-link" name="Land">
  <bpmn:outgoing>f3</bpmn:outgoing>
  <bpmn:linkEventDefinition name="LinkA" />
</bpmn:intermediateCatchEvent>

Validation

Check	Severity
No event definition present	Error
Catch event has anything other than exactly one outgoing sequence flow (BPMN 2.0 §10.5.4 — intermediate events have one input, one output)	Error
Catch event after an event-based gateway has more than one incoming flow	Error
`messageRef` / `signalRef` references an unknown definition	Error

Intermediate throw events

Intermediate throw events emit something — a message, signal, escalation, link, or compensation trigger — and then advance immediately. A throw with no event definition is a pass-through.

Behavior by definition

Definition	Behavior
None	Pure pass-through
Message	Publishes the message with the current scope variables. If `quantum:taskDefinition` is also set, switches to external-job mode (see below)
Signal	Broadcasts the signal to all subscribers
Link	Transfers control to the matching link catch in the same scope. Acts as a goto
Escalation	Throws an escalation up to the nearest matching listener
Compensation	Triggers compensation; `activityRef` can target a specific completed activity

Execution modes (apply to every throw kind)

A throw event with quantum:taskDefinition type="..." switches into worker-driven mode regardless of which event definition is attached: the engine creates a job, the worker performs the actual publish/throw, and the throw advances when the worker reports completion. In this mode the messageRef / escalationRef / etc. become optional — the worker controls what is dispatched.

Mode	When active	Behavior
Direct dispatch	No `quantum:taskDefinition`	Engine publishes / throws immediately and advances
External job	`quantum:taskDefinition type="..."` is set	Engine creates a persistent job; throw advances when the worker completes the job

The same applies to message and escalation end events.

Examples

<!-- Signal throw -->
<bpmn:intermediateThrowEvent id="throw-signal" name="Broadcast Abort">
  <bpmn:incoming>f1</bpmn:incoming>
  <bpmn:outgoing>f2</bpmn:outgoing>
  <bpmn:signalEventDefinition signalRef="Sig_Abort" />
</bpmn:intermediateThrowEvent>

<!-- Escalation throw -->
<bpmn:intermediateThrowEvent id="throw-esc" name="Escalate">
  <bpmn:incoming>f1</bpmn:incoming>
  <bpmn:outgoing>f2</bpmn:outgoing>
  <bpmn:escalationEventDefinition escalationRef="Esc_Review" />
</bpmn:intermediateThrowEvent>

<!-- Link throw (jump source) -->
<bpmn:intermediateThrowEvent id="throw-link" name="Jump">
  <bpmn:incoming>f1</bpmn:incoming>
  <bpmn:linkEventDefinition name="LinkA" />
</bpmn:intermediateThrowEvent>

<!-- Compensation throw — compensate everything completed in scope -->
<bpmn:intermediateThrowEvent id="throw-comp" name="Compensate All">
  <bpmn:incoming>f1</bpmn:incoming>
  <bpmn:outgoing>f2</bpmn:outgoing>
  <bpmn:compensateEventDefinition />
</bpmn:intermediateThrowEvent>

Validation

Check	Severity
`messageRef` / `signalRef` / `escalationRef` references an unknown definition	Error
Message throw with no `messageRef` and no `quantum:taskDefinition` (publish has no name to correlate against)	Error
Escalation throw with no `escalationRef`, no inline `escalationCode`, and no `quantum:taskDefinition` (no listener can match)	Error
Link throw has no matching link catch with the same `name` in the same scope	Error

Boundary events

Boundary events are attached to an activity (task, sub-process, or call activity) and fire while the activity is running.

Attributes

Attribute	Default	Notes
`id`	—	Required
`name`	—	Optional
`attachedToRef`	—	Required. ID of the host activity (must be in the same scope)
`cancelActivity`	`true`	`true` = interrupting (host is cancelled, only the boundary path continues); `false` = non-interrupting (host continues; a parallel token starts from the boundary). Ignored on compensation boundaries

Behavior by definition

Definition	Notes
Message	Fires when a correlated message arrives while the host is active
Timer	`timeDuration` and `timeDate` fire once. `timeCycle` (e.g. `R3/PT1M`) fires repeatedly and is non-interrupting only
Error	Always interrupting. Fires when the host throws a matching error
Signal	Fires when the matching signal is broadcast while the host is active
Escalation	Fires when the host throws a matching escalation
Conditional	Fires when the FEEL `condition` evaluates to `true` while the host is active
Compensation	Marks this boundary as the trigger for a compensation handler. Linked to the handler activity by an `<association>` element. Does not use `cancelActivity` — fires only when compensation is explicitly thrown for the host (after the host has completed), and never cancels the host

Examples

<!-- Interrupting timer boundary: 30-minute timeout -->
<bpmn:boundaryEvent id="timer-boundary" attachedToRef="long-task" cancelActivity="true">
  <bpmn:outgoing>f_timeout</bpmn:outgoing>
  <bpmn:timerEventDefinition>
    <bpmn:timeDuration xsi:type="bpmn:tFormalExpression">PT30M</bpmn:timeDuration>
  </bpmn:timerEventDefinition>
</bpmn:boundaryEvent>

<!-- Non-interrupting message boundary: send a reminder while waiting -->
<bpmn:boundaryEvent id="msg-boundary" attachedToRef="approval-task" cancelActivity="false">
  <bpmn:outgoing>f_notify</bpmn:outgoing>
  <bpmn:messageEventDefinition messageRef="Msg_Reminder" />
</bpmn:boundaryEvent>

<!-- Error boundary: handle a known failure type -->
<bpmn:boundaryEvent id="err-boundary" attachedToRef="service-task" cancelActivity="true">
  <bpmn:outgoing>f_error</bpmn:outgoing>
  <bpmn:errorEventDefinition errorRef="Err_Timeout" />
</bpmn:boundaryEvent>

<!-- Compensation boundary, with handler linked by association -->
<bpmn:boundaryEvent id="comp-boundary" attachedToRef="book-hotel">
  <bpmn:compensateEventDefinition />
</bpmn:boundaryEvent>
<bpmn:serviceTask id="cancel-hotel" name="Cancel Hotel" isForCompensation="true">
  <bpmn:extensionElements>
    <quantum:taskDefinition type="cancel-hotel-worker" />
  </bpmn:extensionElements>
</bpmn:serviceTask>
<bpmn:association id="assoc1" sourceRef="comp-boundary" targetRef="cancel-hotel" />

<!-- Cyclic non-interrupting timer: fire every minute, up to 3 times -->
<bpmn:boundaryEvent id="cycle-boundary" attachedToRef="long-task" cancelActivity="false">
  <bpmn:outgoing>f_tick</bpmn:outgoing>
  <bpmn:timerEventDefinition>
    <bpmn:timeCycle>R3/PT1M</bpmn:timeCycle>
  </bpmn:timerEventDefinition>
</bpmn:boundaryEvent>

Validation

Check	Severity
`attachedToRef` is empty or doesn't resolve to an activity in the same scope	Error
No event definition present	Error
Error boundary has `cancelActivity="false"`	Error
Timer boundary has none of `timeDuration`/`timeDate`/`timeCycle`	Error
Timer boundary uses `timeCycle` while interrupting	Error
Timer boundary mixes `timeCycle` with `timeDuration` or `timeDate`	Warning (`timeCycle` wins)
Conditional boundary has empty `condition`	Error
Compensation boundary has no associated handler activity	Error
Compensation handler is not marked `isForCompensation="true"`	Error
`messageRef` / `signalRef` / `errorRef` / `escalationRef` references an unknown definition	Error

Event definitions​

Position × definition compatibility​

Start events​

Attributes​

Auto-start behavior​

Examples​

Validation​

End events​

Behavior by definition​

Examples​

Validation​

Intermediate catch events​

Behavior by definition​

Examples​

Validation​

Intermediate throw events​

Behavior by definition​

Execution modes (apply to every throw kind)​

Examples​

Validation​

Boundary events​

Attributes​

Behavior by definition​

Examples​

Validation​

Event definitions

Position × definition compatibility

Start events

Attributes

Auto-start behavior

Examples

Validation

End events

Behavior by definition

Examples

Validation

Intermediate catch events

Behavior by definition

Examples

Validation

Intermediate throw events

Behavior by definition

Execution modes (apply to every throw kind)

Examples

Validation

Boundary events

Attributes

Behavior by definition

Examples

Validation