An exclusive gateway, or XOR gateway is used to model a decision in a process definition.
When the execution of a workflow arrives at this gateway, all outgoing sequence flows are evaluated in the order in which they are defined. The sequence flow whose condition evaluates to true, is selected for propagating the token flow.
- In general in BPMN 2.0, all sequence flows whose conditions evaluate to true are selected to continue in a parallel way. When using an exclusive gateway, only one sequence flow is selected.
- When multiple sequence flows have conditions which evaluate to true, only the first one defined is selected to continue the process.
- If no sequence flow can be selected, an exception will be thrown. To ensure a sequence flow will always be selected, have no condition on one of your flows. No condition will always evaluate to true.