Exclusive Gateway (XOR)

Routes execution to exactly one outgoing path based on conditions.

<exclusiveGateway id="checkAmount" name="Amount OK?" default="rejectFlow" />
<sequenceFlow id="approveFlow" sourceRef="checkAmount" targetRef="approve">
  <conditionExpression>${amount} > 0</conditionExpression>
</sequenceFlow>
<sequenceFlow id="rejectFlow" sourceRef="checkAmount" targetRef="reject" />

Decision algorithm

The engine evaluates outgoing flows in document order:

1. For each flow that has a condition expression: evaluate the condition against current variables
2. The first flow whose condition evaluates to true is taken — remaining flows are not evaluated
3. If no conditional flow matched and an unconditioned flow exists, that flow is taken
4. If no conditional flow matched but a default flow is configured (default attribute), the default flow is taken
5. If nothing matched: the instance transitions to Failed with a NoMatchingCondition error

Order matters. Conditions are evaluated in the order they appear in the XML, so place more specific conditions before broader ones.

Condition expression syntax

Operators:  ==  !=  >  <  >=  <=  &&  ||  !

Variable reference:
  ${varName}   or   varName

Literal values:
  "string"     'string'    123    3.14    true    false    null

Examples:
  ${amount} > 0
  status == 'approved' && amount < 1000
  !rejected

Type coercion rules:

• "42" == 42 → true (string coerced to number for comparison)
• 2 == 2.0 → true (integer and float compared as float)
• An undefined variable evaluates to false (logged as a warning)