Exclusive gateway

An exclusive gateway (aka XOR-gateway) allows to make a decision based on data (i.e. on workflow instance variables).

If an exclusive gateway has multiple outgoing sequence flows then all sequence flows, except one, must have a conditionExpression to define when the flow is taken. The gateway can have one sequence flow without conditionExpression which must be defined as the default flow.

When an exclusive gateway is entered then the conditionExpressions are evaluated. The workflow instance takes the first sequence flow that condition is fulfilled.

If no condition is fulfilled then it takes the default flow of the gateway. In case the gateway has no default flow, an incident is created.

An exclusive gateway can also be used to join multiple incoming flows to one, in order to improve the readability of the BPMN. A joining gateway has a pass-through semantic. It doesn't merge the 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 workflow instance 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 (and) or conjunction (or).

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" />

Using the BPMN modeler

Adding an exclusive gateway with two outgoing sequence flows:

Workflow lifecycle

Workflow instance records of an exclusive gateway:

Intent	Element Id	Element Type
ELEMENT_ACTIVATING	shipping-gateway	EXCLUSIVE_GATEWAY
ELEMENT_ACTIVATED	shipping-gateway	EXCLUSIVE_GATEWAY
ELEMENT_COMPLETING	shipping-gateway	EXCLUSIVE_GATEWAY
ELEMENT_COMPLETED	shipping-gateway	EXCLUSIVE_GATEWAY
SEQUENCE_FLOW_TAKEN	priceGreaterThan100	SEQUENCE_FLOW

References:

• Expressions
• Incidents