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Version: 8.10 (unreleased)

Exclusive gateway

An exclusive gateway (or XOR-gateway) selects one outgoing sequence flow based on data such as process variables.

process

For an exclusive gateway with multiple outgoing sequence flows:

  • All but one sequence flow must have a conditionExpression.
  • The remaining sequence flow can omit the conditionExpression, but the gateway must define it as the default flow.
  • Leaving the conditionExpression empty does not automatically make a sequence flow the default flow. In Modeler, set the exclusive gateway's default flow in the gateway properties by selecting the outgoing sequence flow to use as the default.
  • When a process instance reaches the gateway, the system evaluates the conditionExpression values in BPMN XML order and takes the first sequence flow whose condition is fulfilled.
    • If no condition is fulfilled, the process instance takes the default flow. The default flow should not have a condition, so the system does not evaluate it.
    • If no condition is fulfilled and the gateway has no default flow, an incident is created.

For example, if one sequence flow uses the condition = totalPrice > 100, you can set another outgoing sequence flow as the gateway's default flow to handle all remaining cases where totalPrice <= 100.

An exclusive gateway can also join multiple incoming flows to improve BPMN readability. A joining gateway has pass-through semantics and does not merge incoming concurrent flows like a parallel gateway.

Conditions​

A conditionExpression defines when a flow is taken. It is a boolean expression that can access the process variables and compare them with literals or other variables. The condition is fulfilled when the expression returns true.

Multiple boolean values or comparisons can be combined as disjunction (or) or conjunction (and).

For example:

= totalPrice > 100

= order.customer = "Paul"

= orderCount > 15 or totalPrice > 50

= valid and orderCount > 0

Additional resources​

XML representation​

An exclusive gateway with two outgoing sequence flows:

<bpmn:exclusiveGateway id="exclusiveGateway" default="else" />

<bpmn:sequenceFlow id="priceGreaterThan100" name="totalPrice &#62; 100"
  sourceRef="exclusiveGateway" targetRef="shipParcelWithInsurance">
  <bpmn:conditionExpression xsi:type="bpmn:tFormalExpression">
    = totalPrice &gt; 100
  </bpmn:conditionExpression>
</bpmn:sequenceFlow>

<bpmn:sequenceFlow id="else" name="else"
  sourceRef="exclusiveGateway" targetRef="shipParcel" />

References​