BPMN 2.0 Elements

Priostack supports the BPMN 2.0 specification. This page is the complete reference for all supported elements, including their XML representation and usage notes.

Start Events

Element	Symbol	Description
None Start Event	○	Process begins immediately when started via API. No trigger required.
Message Start Event	✉○	Process is triggered when a named message is received. Used for event-driven process starts.
Timer Start Event	⏱○	Process is triggered on a schedule (ISO 8601 duration, date, or cycle). Example: `R/PT1H` = every hour.
Signal Start Event	△○	Process is triggered when a named signal is broadcast. Multiple processes can listen for the same signal.

<!-- None Start Event -->
<startEvent id="start" name="Order Received" />

<!-- Timer Start Event (every day at midnight) -->
<startEvent id="dailyStart">
  <timerEventDefinition>
    <timeCycle xsi:type="tFormalExpression">R/P1D</timeCycle>
  </timerEventDefinition>
</startEvent>

<!-- Message Start Event -->
<startEvent id="msgStart">
  <messageEventDefinition messageRef="orderMessage" />
</startEvent>

End Events

Element	Symbol	Description
None End Event	●	Process path terminates normally. If all tokens reach end events, the instance completes.
Message End Event	✉●	Sends a message to an external participant when the process path ends.
Error End Event	✖●	Throws a named error that can be caught by a boundary error event on a calling process.
Terminate End Event	⬛●	Immediately terminates all running paths in the current scope, not just the current token.

<!-- Error End Event -->
<endEvent id="errorEnd">
  <errorEventDefinition errorRef="paymentError" />
</endEvent>

<error id="paymentError" name="Payment Failed" errorCode="PAYMENT_FAILED" />

Tasks

Element	Description
Service Task	Executed by an external worker. The engine creates a job; the worker activates and completes it. Required extension: `zeebe:taskDefinition type="..."`
User Task	Requires a human to complete via the Tasklist. Optional assignee, candidate groups, and due date via `zeebe:userTask` extension.
Script Task	Evaluates a FEEL expression inline without an external worker. Useful for simple data transformations.
Send Task	Sends a message to an external system or to a Message Catch Event in another process.
Receive Task	Waits for a message correlated by a message name and correlation key.
Call Activity	Invokes another process definition as a sub-process. Variables can be mapped in/out.

<!-- Service Task -->
<serviceTask id="validateOrder" name="Validate Order">
  <extensionElements>
    <zeebe:taskDefinition type="validate-order" retries="3" />
    <zeebe:ioMapping>
      <zeebe:input source="=orderId" target="orderId" />
      <zeebe:output source="=valid" target="orderValid" />
    </zeebe:ioMapping>
  </extensionElements>
</serviceTask>

<!-- User Task -->
<userTask id="reviewTask" name="Review Order">
  <extensionElements>
    <zeebe:userTask>
      <zeebe:assignee>=reviewer</zeebe:assignee>
      <zeebe:candidateGroups>managers</zeebe:candidateGroups>
    </zeebe:userTask>
  </extensionElements>
</userTask>

<!-- Call Activity -->
<callActivity id="callPayment" name="Process Payment">
  <extensionElements>
    <zeebe:calledElement processId="payment-process" />
    <zeebe:ioMapping>
      <zeebe:input source="=amount" target="amount" />
      <zeebe:input source="=currency" target="currency" />
      <zeebe:output source="=transactionId" target="paymentTransactionId" />
    </zeebe:ioMapping>
  </extensionElements>
</callActivity>

Gateways

Element	Symbol	Description
Exclusive Gateway (XOR)	✕	Exactly one outgoing path is taken. Each sequence flow has a FEEL condition; the first true condition wins. A default flow handles the fallback case.
Parallel Gateway (AND)	+	All outgoing paths are activated simultaneously (split). When used as a join, waits for all incoming tokens before continuing.
Inclusive Gateway (OR)	○	One or more outgoing paths are taken based on FEEL conditions. The join waits for all activated paths.
Event-Based Gateway	◇	Waits for the first of several events (messages, timers, signals) to occur, then follows that path.

<!-- Exclusive Gateway -->
<exclusiveGateway id="checkAmount" name="Amount OK?" />
<sequenceFlow sourceRef="checkAmount" targetRef="approve">
  <conditionExpression>=amount <= 1000</conditionExpression>
</sequenceFlow>
<sequenceFlow sourceRef="checkAmount" targetRef="managerApproval">
  <conditionExpression>=amount > 1000</conditionExpression>
</sequenceFlow>

<!-- Parallel Gateway (split) -->
<parallelGateway id="splitTasks" name="Run in Parallel" />

<!-- Event-Based Gateway -->
<eventBasedGateway id="waitForEvent" />

Intermediate Events

Element	Description
Intermediate Timer Catch	Pauses execution for a duration or until a specific date/time.
Intermediate Message Catch	Waits for a correlated message before continuing. Requires a correlation key.
Intermediate Signal Catch	Waits for a named signal to be broadcast.
Intermediate Message Throw	Sends a message to another process or external system mid-flow.

Boundary Events

Boundary events attach to tasks and trigger alternative paths when the attached event fires. They can be interrupting (cancel the task) or non-interrupting (run in parallel).

Type	Description
Timer Boundary	Escalates if the task takes longer than the defined duration.
Error Boundary	Catches errors thrown by the task or its sub-process. Always interrupting.
Message Boundary	Catches a correlated message while the task is active.
Signal Boundary	Catches a broadcast signal while the task is active.

<!-- Timer Boundary Event (escalate after 1 hour) -->
<boundaryEvent id="timeout" attachedToRef="reviewTask" cancelActivity="true">
  <timerEventDefinition>
    <timeDuration xsi:type="tFormalExpression">PT1H</timeDuration>
  </timerEventDefinition>
</boundaryEvent>
<sequenceFlow sourceRef="timeout" targetRef="escalate" />

<!-- Error Boundary Event -->
<boundaryEvent id="paymentFailed" attachedToRef="processPayment">
  <errorEventDefinition errorRef="paymentError" />
</boundaryEvent>

Subprocess

A subprocess is an embedded process within the parent process. It groups tasks and has its own scope for variables and boundary events.

<subProcess id="fulfillmentSubProcess" name="Fulfillment">
  <startEvent id="subStart" />
  <serviceTask id="pickItems" name="Pick Items">
    <extensionElements>
      <zeebe:taskDefinition type="pick-items" />
    </extensionElements>
  </serviceTask>
  <serviceTask id="packItems" name="Pack Items">
    <extensionElements>
      <zeebe:taskDefinition type="pack-items" />
    </extensionElements>
  </serviceTask>
  <endEvent id="subEnd" />
  <sequenceFlow sourceRef="subStart" targetRef="pickItems" />
  <sequenceFlow sourceRef="pickItems" targetRef="packItems" />
  <sequenceFlow sourceRef="packItems" targetRef="subEnd" />
</subProcess>

Lanes

Lanes visually partition a pool to represent different participants, roles, or systems. They have no execution semantics — they are for modeling clarity only.

<laneSet id="laneSet1">
  <lane id="customerLane" name="Customer">
    <flowNodeRef>start</flowNodeRef>
    <flowNodeRef>submitOrder</flowNodeRef>
  </lane>
  <lane id="systemLane" name="System">
    <flowNodeRef>validateOrder</flowNodeRef>
    <flowNodeRef>processPayment</flowNodeRef>
    <flowNodeRef>end</flowNodeRef>
  </lane>
</laneSet>

Tip: Use the Priostack Designer to visually build BPMN diagrams. The designer uses bpmn-js and generates valid BPMN 2.0 XML that can be deployed directly via the API.