Exclusive Gateway (XOR)

The Exclusive Gateway (also known as XOR Gateway) makes either/or decisions by choosing exactly ONE path from multiple options based on conditions.

Symbol

In BPMN diagrams, it's shown as a diamond with an "X" marker or empty diamond.

When to Use

Use Exclusive Gateways when you need to:

Make approve/reject decisions
Route based on amount thresholds
Branch based on risk levels (Low/Medium/High)
Direct to different approval levels
Any scenario where only ONE path should execute

Visual Example

Result: Only ONE approval task executes (not both)

Implementation Options

There are two ways to implement Exclusive Gateways:

Option 1: Gateway-Level Condition (Recommended)

The gateway itself contains a script that returns which flow to take.

BPMN XML Example

<bpmn:exclusiveGateway id="Gateway_CheckAmount" 
                       name="Check Loan Amount" 
                       default="Flow_Standard">
  <bpmn:incoming>Flow_In</bpmn:incoming>
  <bpmn:outgoing>Flow_HighValue</bpmn:outgoing>
  <bpmn:outgoing>Flow_Standard</bpmn:outgoing>
  
  <!-- Gateway-level condition -->
  <bpmn:extensionElements>
    <custom:properties>
      <custom:property name="Condition" value="
        // Return the flow name or ID to take
        if (loanAmount > 100000) {
          return 'Flow_HighValue';
        } else {
          return 'Flow_Standard';
        }
      " />
    </custom:properties>
  </bpmn:extensionElements>
</bpmn:exclusiveGateway>

<!-- Define the flows -->
<bpmn:sequenceFlow id="Flow_HighValue" 
                   name="High Value (>$100k)" 
                   sourceRef="Gateway_CheckAmount" 
                   targetRef="Task_SeniorApproval" />
                   
<bpmn:sequenceFlow id="Flow_Standard" 
                   name="Standard Amount" 
                   sourceRef="Gateway_CheckAmount" 
                   targetRef="Task_StandardApproval" />

Fields Reference

Field	Location	Required	Description	Example
`id`	Gateway element	✅ Yes	Unique gateway identifier	`Gateway_CheckAmount`
`name`	Gateway element	⚪ Optional	Descriptive name for the gateway	`"Check Loan Amount"`
`default`	Gateway element	✅ Recommended	Flow ID to take if condition fails/no match	`Flow_Standard`
`Condition`	Extension property	✅ Yes (Option 1)	JavaScript that returns flow name/ID	See example
`incoming`	Gateway element	✅ Yes	Incoming sequence flow ID	`Flow_In`
`outgoing`	Gateway element	✅ Yes	List of outgoing flow IDs	Multiple `<outgoing>` tags

Script Context

Your Condition script has access to:

All process variables: loanAmount, customerName, creditScore, etc.
Return value: Must be a string matching a flow id or name

Example Scripts:

// Simple threshold
return amount > 50000 ? 'Flow_Senior' : 'Flow_Standard';

// Multiple conditions
if (creditScore >= 720) {
  return 'Flow_Approved';
} else if (creditScore >= 650) {
  return 'Flow_Review';
} else {
  return 'Flow_Rejected';
}

// Complex logic
const risk = calculateRiskScore(creditScore, debtToIncome, loanAmount);
if (risk < 30) return 'Flow_LowRisk';
if (risk < 60) return 'Flow_MediumRisk';
return 'Flow_HighRisk';

Execution Flow

Process reaches gateway
Engine executes Condition script
Script returns flow name/ID (e.g., 'Flow_HighValue')
Engine finds matching flow by id or name
Process continues down that flow
Other flows are NOT executed

Execution Log Example

[GATEWAY] Evaluating exclusive gateway: Gateway_CheckAmount (Check Loan Amount)
[GATEWAY] Available paths: 2
[GATEWAY]   → Flow_HighValue: 'High Value (>$100k)' → Task_SeniorApproval
[GATEWAY]   → Flow_Standard: 'Standard Amount' → Task_StandardApproval (DEFAULT)
[GATEWAY] Executing gateway-level condition script
[GATEWAY] Process variables: loanAmount=150000, creditScore=720
[GATEWAY] ✓ Condition script returned: 'Flow_HighValue'
[GATEWAY] ✓ DECISION: Taking flow 'Flow_HighValue' → Task_SeniorApproval
[GATEWAY] Moving to element: Task_SeniorApproval

Option 2: Flow-Level Conditions

Each outgoing flow has its own condition expression. The first flow whose condition evaluates to true is taken.

BPMN XML Example

<bpmn:exclusiveGateway id="Gateway_RiskLevel" 
                       name="Risk Assessment" 
                       default="Flow_Rejected">
  <bpmn:incoming>Flow_In</bpmn:incoming>
  <bpmn:outgoing>Flow_LowRisk</bpmn:outgoing>
  <bpmn:outgoing>Flow_MediumRisk</bpmn:outgoing>
  <bpmn:outgoing>Flow_HighRisk</bpmn:outgoing>
  <bpmn:outgoing>Flow_Rejected</bpmn:outgoing>
</bpmn:exclusiveGateway>

<!-- Flow 1: Low Risk -->
<bpmn:sequenceFlow id="Flow_LowRisk" 
                   name="Low Risk" 
                   sourceRef="Gateway_RiskLevel" 
                   targetRef="Task_AutoApprove">
  <bpmn:conditionExpression>
    creditScore >= 720 &amp;&amp; debtToIncomeRatio &lt; 36
  </bpmn:conditionExpression>
</bpmn:sequenceFlow>

<!-- Flow 2: Medium Risk -->
<bpmn:sequenceFlow id="Flow_MediumRisk" 
                   name="Medium Risk"
                   sourceRef="Gateway_RiskLevel" 
                   targetRef="Task_OfficerReview">
  <bpmn:conditionExpression>
    creditScore >= 650 &amp;&amp; creditScore &lt; 720
  </bpmn:conditionExpression>
</bpmn:sequenceFlow>

<!-- Flow 3: High Risk -->
<bpmn:sequenceFlow id="Flow_HighRisk" 
                   name="High Risk"
                   sourceRef="Gateway_RiskLevel" 
                   targetRef="Task_ManagerReview">
  <bpmn:conditionExpression>
    creditScore >= 580 &amp;&amp; creditScore &lt; 650
  </bpmn:conditionExpression>
</bpmn:sequenceFlow>

<!-- Default Flow: No condition (fallback) -->
<bpmn:sequenceFlow id="Flow_Rejected" 
                   name="Rejected"
                   sourceRef="Gateway_RiskLevel" 
                   targetRef="Task_NotifyRejection" />

Fields Reference

Field	Location	Required	Description	Example
`conditionExpression`	Inside `<sequenceFlow>`	⚪ Optional	Boolean JavaScript expression	`creditScore >= 720`
`default`	Gateway element	✅ Recommended	Flow ID if no conditions match	`Flow_Rejected`

Condition Expression Syntax

Flow conditions must return true or false:

// Simple comparison
creditScore >= 720

// Multiple conditions (use XML entities)
creditScore >= 720 &amp;&amp; debtToIncomeRatio &lt; 36

// Complex expression
(amount > 50000 &amp;&amp; creditScore >= 700) || approvalOverride === true

XML Special Characters:

Character	XML Entity
`&&`	`&&`
`<`	`<`
`>`	`>`
`"`	`"`

Evaluation Order

Engine evaluates flows in the order they appear in XML (skips default flow)
First condition that returns true wins
If no conditions match, takes the default flow
If no default and no matches → process error

Execution Log Example

[GATEWAY] Evaluating exclusive gateway: Gateway_RiskLevel (Risk Assessment)
[GATEWAY] Available paths: 4
[GATEWAY]   → Flow_LowRisk: 'Low Risk' → Task_AutoApprove
[GATEWAY]   → Flow_MediumRisk: 'Medium Risk' → Task_OfficerReview
[GATEWAY]   → Flow_HighRisk: 'High Risk' → Task_ManagerReview
[GATEWAY]   → Flow_Rejected: 'Rejected' → Task_NotifyRejection (DEFAULT)
[GATEWAY] Evaluating flow conditions...
[GATEWAY]   Flow_LowRisk: false (creditScore=680, debtToIncomeRatio=42)
[GATEWAY]   Flow_MediumRisk: true
[GATEWAY] ✓ DECISION: Taking flow 'Flow_MediumRisk' → Task_OfficerReview
[GATEWAY] Moving to element: Task_OfficerReview

Use Cases

Use Case 1: Amount-Based Approval Routing

Scenario: Route loan applications to different approval levels based on amount.

Requirements:

Loans < $50K → Standard approval
Loans $50K-$250K → Senior approval
Loans > $250K → Executive approval

Implementation:

<bpmn:exclusiveGateway id="Gateway_Amount" default="Flow_Standard">
  <bpmn:extensionElements>
    <custom:properties>
      <custom:property name="Condition" value="
        if (loanAmount > 250000) return 'Flow_Executive';
        if (loanAmount > 50000) return 'Flow_Senior';
        return 'Flow_Standard';
      " />
    </custom:properties>
  </bpmn:extensionElements>
  <bpmn:outgoing>Flow_Executive</bpmn:outgoing>
  <bpmn:outgoing>Flow_Senior</bpmn:outgoing>
  <bpmn:outgoing>Flow_Standard</bpmn:outgoing>
</bpmn:exclusiveGateway>

Visual Flow:

Use Case 2: Risk-Based Routing

Scenario: Different handling based on calculated risk score.

Requirements:

Low risk (score < 30) → Auto-approve
Medium risk (30-60) → Officer review
High risk (60-80) → Manager review
Very high risk (>80) → Auto-reject

Implementation:

<bpmn:exclusiveGateway id="Gateway_Risk" default="Flow_Reject">
  <bpmn:outgoing>Flow_Auto</bpmn:outgoing>
  <bpmn:outgoing>Flow_Officer</bpmn:outgoing>
  <bpmn:outgoing>Flow_Manager</bpmn:outgoing>
  <bpmn:outgoing>Flow_Reject</bpmn:outgoing>
</bpmn:exclusiveGateway>

<bpmn:sequenceFlow id="Flow_Auto" sourceRef="Gateway_Risk" targetRef="Task_Approve">
  <bpmn:conditionExpression>riskScore &lt; 30</bpmn:conditionExpression>
</bpmn:sequenceFlow>

<bpmn:sequenceFlow id="Flow_Officer" sourceRef="Gateway_Risk" targetRef="Task_Officer">
  <bpmn:conditionExpression>riskScore >= 30 &amp;&amp; riskScore &lt; 60</bpmn:conditionExpression>
</bpmn:sequenceFlow>

<bpmn:sequenceFlow id="Flow_Manager" sourceRef="Gateway_Risk" targetRef="Task_Manager">
  <bpmn:conditionExpression>riskScore >= 60 &amp;&amp; riskScore &lt;= 80</bpmn:conditionExpression>
</bpmn:sequenceFlow>

Use Case 3: Status-Based Branching

Scenario: Handle different customer account statuses differently.

<bpmn:exclusiveGateway id="Gateway_Status">
  <bpmn:extensionElements>
    <custom:properties>
      <custom:property name="Condition" value="
        switch(accountStatus) {
          case 'ACTIVE': return 'Flow_Process';
          case 'SUSPENDED': return 'Flow_Review';
          case 'CLOSED': return 'Flow_Reject';
          case 'PENDING': return 'Flow_Verify';
          default: return 'Flow_Error';
        }
      " />
    </custom:properties>
  </bpmn:extensionElements>
</bpmn:exclusiveGateway>

Execution Diagram

┌─────────────────────────────────────────┐
│ 1. Process reaches Exclusive Gateway   │
└────────────────┬────────────────────────┘
                 │
                 ▼
┌─────────────────────────────────────────┐
│ 2. Has gateway-level Condition?         │
└─────┬────────────────────────┬──────────┘
      │ YES                    │ NO
      ▼                        ▼
┌──────────────────┐  ┌────────────────────┐
│ Execute script   │  │ Evaluate each      │
│ Get flow name/ID │  │ flow's condition   │
└─────┬────────────┘  └────────┬───────────┘
      │                        │
      └────────┬───────────────┘
               ▼
    ┌──────────────────────┐
    │ Find matching flow   │
    └──────────┬───────────┘
               │
         ┌─────┴─────┐
         │ Found?    │
         └─┬───────┬─┘
      YES  │       │  NO
           ▼       ▼
    ┌──────────┐ ┌─────────────┐
    │ Take it  │ │ Take default│
    └────┬─────┘ └──────┬──────┘
         │              │
         └──────┬───────┘
                ▼
    ┌────────────────────────┐
    │ Continue on that path  │
    └────────────────────────┘

Best Practices

✅ DO:

Always set a default flow to handle unexpected cases
Use descriptive flow names: "High Value (>$100k)" not "Flow_1"
Keep conditions simple - move complex logic to ScriptTask before gateway
Return exact flow IDs or names from gateway condition
Test all branches to ensure each path is reachable

❌ DON'T:

Don't forget the default flow - process will error if no condition matches
Don't use complex expressions directly in conditions - hard to debug
Don't mix gateway-level and flow-level conditions - choose one approach
Don't return flow names that don't exist - process will error
Don't make multiple paths execute - use Inclusive or Parallel for that

Common Patterns

Pattern: Pre-Calculate Decision Value

Instead of complex gateway logic, calculate the decision value beforehand:

<!-- 1. Calculate decision value -->
<bpmn:scriptTask id="Task_Calculate" name="Calculate Route">
  <bpmn:extensionElements>
    <custom:properties>
      <custom:property name="Script" value="
        // Complex logic here
        const riskScore = calculateRisk(creditScore, income, debt);
        const employmentYears = calculateEmployment(startDate);
        
        // Set simple decision variable
        if (riskScore < 30 &amp;&amp; employmentYears > 2) {
          approvalRoute = 'AUTO';
        } else if (riskScore < 60) {
          approvalRoute = 'OFFICER';
        } else {
          approvalRoute = 'MANAGER';
        }
      " />
    </custom:properties>
  </bpmn:extensionElements>
</bpmn:scriptTask>

<!-- 2. Simple gateway uses calculated value -->
<bpmn:exclusiveGateway id="Gateway_Route">
  <bpmn:extensionElements>
    <custom:properties>
      <custom:property name="Condition" value="
        // Simple lookup
        return 'Flow_' + approvalRoute;
      " />
    </custom:properties>
  </bpmn:extensionElements>
</bpmn:exclusiveGateway>

Benefits:

Gateway logic is simple and debuggable
Complex calculation logic is in one place
Easy to unit test the calculation separately

Troubleshooting

Issue: Gateway takes default flow when it shouldn't

Symptoms: Always goes to default path even when other conditions should match

Possible Causes:

Condition script error

// ❌ Wrong - typo in variable name
return loanAmmount > 50000 ? 'Flow_High' : 'Flow_Low';

// ✅ Correct
return loanAmount > 50000 ? 'Flow_High' : 'Flow_Low';

Flow name mismatch

// ❌ Wrong - returns name that doesn't exist
return 'HighValue';  // But flow is named 'Flow_HighValue'

// ✅ Correct - match exact flow id or name
return 'Flow_HighValue';

Flow-level condition syntax error

<!-- ❌ Wrong - missing XML entity -->
<bpmn:conditionExpression>
  amount > 50000 && creditScore >= 700
</bpmn:conditionExpression>

<!-- ✅ Correct - use XML entities -->
<bpmn:conditionExpression>
  amount > 50000 &amp;&amp; creditScore >= 700
</bpmn:conditionExpression>

Check the logs:

[GATEWAY] ✗ WARNING: Condition returned 'xyz' but no matching flow found
[GATEWAY] Available flow IDs: Flow_HighValue, Flow_Standard
[GATEWAY] Available flow names: 'High Value', 'Standard'
[GATEWAY] ⚠ Falling back to default flow: Flow_Standard

Issue: Process throws error at gateway

Symptoms: Process execution fails with error at gateway

Possible Causes:

No default flow and no condition matches

<!-- ❌ Wrong - no default, condition can fail -->
<bpmn:exclusiveGateway id="Gateway_1">
  <bpmn:outgoing>Flow_A</bpmn:outgoing>
  <bpmn:outgoing>Flow_B</bpmn:outgoing>
</bpmn:exclusiveGateway>

<!-- ✅ Correct - always have default -->
<bpmn:exclusiveGateway id="Gateway_1" default="Flow_B">

Gateway has no outgoing flows

<!-- ❌ Wrong - gateway leads nowhere -->
<bpmn:exclusiveGateway id="Gateway_1">
  <bpmn:incoming>Flow_In</bpmn:incoming>
</bpmn:exclusiveGateway>

<!-- ✅ Correct - at least one outgoing -->
<bpmn:exclusiveGateway id="Gateway_1">
  <bpmn:incoming>Flow_In</bpmn:incoming>
  <bpmn:outgoing>Flow_Out</bpmn:outgoing>
</bpmn:exclusiveGateway>

Issue: Variable is undefined in condition

Symptoms: Condition fails because variable doesn't exist

Solution: Set variables before gateway:

<!-- Prepare variables first -->
<bpmn:scriptTask id="Task_Prepare">
  <bpmn:extensionElements>
    <custom:properties>
      <custom:property name="Script" value="
        loanAmount = loanAmount || 0;  // Default value
        creditScore = creditScore || 0;
      " />
    </custom:properties>
  </bpmn:extensionElements>
</bpmn:scriptTask>

<bpmn:sequenceFlow sourceRef="Task_Prepare" targetRef="Gateway_Check" />

Summary

Exclusive Gateway (XOR):

✅ Chooses exactly ONE path from multiple options
✅ Use for either/or decisions, routing, branching
✅ Two implementation options: gateway-level condition OR flow-level conditions
✅ Always set a default flow
✅ Keep conditions simple and testable

Next Steps:

See Parallel Gateway for executing multiple paths simultaneously
See Inclusive Gateway for conditional multi-path execution
Browse Use Cases for more real-world examples
Check Troubleshooting if you encounter issues

Symbol​

When to Use​

Visual Example​

Implementation Options​

Option 1: Gateway-Level Condition (Recommended)​

BPMN XML Example​

Fields Reference​

Script Context​

Execution Flow​

Execution Log Example​

Option 2: Flow-Level Conditions​

BPMN XML Example​

Fields Reference​

Condition Expression Syntax​

Evaluation Order​

Execution Log Example​

Use Cases​

Use Case 1: Amount-Based Approval Routing​

Use Case 2: Risk-Based Routing​

Use Case 3: Status-Based Branching​

Execution Diagram​

Best Practices​

✅ DO:​

❌ DON'T:​

Common Patterns​

Pattern: Pre-Calculate Decision Value​

Troubleshooting​

Issue: Gateway takes default flow when it shouldn't​

Issue: Process throws error at gateway​

Issue: Variable is undefined in condition​

Summary​

Symbol

When to Use

Visual Example

Implementation Options

Option 1: Gateway-Level Condition (Recommended)

BPMN XML Example

Fields Reference

Script Context

Execution Flow

Execution Log Example

Option 2: Flow-Level Conditions

BPMN XML Example

Fields Reference

Condition Expression Syntax

Evaluation Order

Execution Log Example

Use Cases

Use Case 1: Amount-Based Approval Routing

Use Case 2: Risk-Based Routing

Use Case 3: Status-Based Branching

Execution Diagram

Best Practices

✅ DO:

❌ DON'T:

Common Patterns

Pattern: Pre-Calculate Decision Value

Troubleshooting

Issue: Gateway takes default flow when it shouldn't

Issue: Process throws error at gateway

Issue: Variable is undefined in condition

Summary