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Integrating QuantumDMN with Camunda 8

· 9 min read
Richard Bízik
Richard Bízik
Creator of QuantumDMN

Camunda 8 is a powerful process orchestration platform, but when it comes to complex decision logic, its built-in DMN engine can sometimes feel limiting. It supports a subset of the DMN 1.3 standard (Conformance Level 2ish), which is great for simple decision tables but struggles with advanced requirements like:

  • Complex FEEL expressions, list handling, and Contexts
  • BKMs (Business Knowledge Models) and Boxed Expressions
  • Cross-decision dependencies and invocations
  • Stateful knowledge (e.g., historical data for KPIs)
  • Deep insights into decision execution

Enter QuantumDMN. We provide full DMN 1.5 Conformance Level 3 support, meaning you can run any valid DMN model—including those with functions, list filtering, and complex contexts. Plus, our engine offers unparalleled transparency into how a decision was reached.

In this post, we'll show you how to get the best of both worlds: Camunda 8 for BPMN orchestration and QuantumDMN for advanced decisioning.

Architecture​

The integration pattern is straightforward:

  1. Camunda 8 (Zeebe) orchestrates the process.
  2. A Business Rule Task in BPMN creates a job with a specific type (e.g., quantumdmn-decision).
  3. A Java Worker subscribes to this job type.
  4. The Worker calls the QuantumDMN API to evaluate the decision.
  5. The result is returned to the process as variables.

Prerequisites​

  • Java 17+
  • Maven
  • Camunda 8 Account (SaaS or Self-Managed)
  • QuantumDMN Account (or local instance)

Setting up Authentication (SaaS)​

To authenticate your worker with QuantumDMN, you'll need a Service Account.

  1. Create a Service Account:

    • Log in to your Zitadel instance (e.g., auth.quantumdmn.com).
    • Navigate to Users and create a new Service Account.
    • Set the Access Token Type to JWT.

  2. Generate a Key File:

    • In the Service Account details in Zitadel, go to Keys.
    • Generate a new JSON key file with an expiration date.
    • Save this file—you'll need its path for the QUANTUMDMN_KEY_FILE configuration.

  3. Grant Permissions:

    • Go to Roles (or Grants) and ensure the Service Account has the User role for the dmn-engine project.
    • Navigate to the QuantumDMN Platform.
    • Grant the Service Account Executor access to the specific project where your definitions are located.

The Example Project​

You can find the full source code for this example on GitHub.

1. The BPMN Process​

We start with a simple BPMN process in Camunda. It has a Service Task configured to call our external worker.

BPMN Process

BPMN Process XML
<?xml version="1.0" encoding="UTF-8"?>
<bpmn:definitions xmlns:bpmn="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:dc="http://www.omg.org/spec/DD/20100524/DC" xmlns:zeebe="http://camunda.org/schema/zeebe/1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:di="http://www.omg.org/spec/DD/20100524/DI" xmlns:modeler="http://camunda.org/schema/modeler/1.0" id="Definitions_1aa8dca" targetNamespace="http://bpmn.io/schema/bpmn" exporter="Camunda Modeler" exporterVersion="5.38.1" modeler:executionPlatform="Camunda Cloud" modeler:executionPlatformVersion="8.7.0">
  <bpmn:process id="Process_04iiy32" isExecutable="true">
    <bpmn:startEvent id="StartEvent">
      <bpmn:outgoing>Flow_0nvvwuq</bpmn:outgoing>
    </bpmn:startEvent>
    <bpmn:businessRuleTask id="Activity_1ijk7i6" name="QuantumDMN&#10;simple_decision">
      <bpmn:extensionElements>
        <zeebe:taskDefinition type="quantumdmn-decision" />
        <zeebe:ioMapping>
          <zeebe:input source="=process_age" target="age" />
          <zeebe:output source="=decisionResult" target="approved" />
        </zeebe:ioMapping>
        <zeebe:taskHeaders>
          <zeebe:header key="xmlDefinitionID" value="allowAge_model" />
          <zeebe:header key="decisionName" value="AllowAgeDecision" />
        </zeebe:taskHeaders>
      </bpmn:extensionElements>
      <bpmn:incoming>Flow_0nvvwuq</bpmn:incoming>
      <bpmn:outgoing>Flow_0ztg4mq</bpmn:outgoing>
    </bpmn:businessRuleTask>
    <bpmn:sequenceFlow id="Flow_0nvvwuq" sourceRef="StartEvent" targetRef="Activity_1ijk7i6" />
    <bpmn:exclusiveGateway id="Gateway_13vlylm" default="Flow_0e7fpjw">
      <bpmn:incoming>Flow_0ztg4mq</bpmn:incoming>
      <bpmn:outgoing>Flow_0kt470w</bpmn:outgoing>
      <bpmn:outgoing>Flow_0e7fpjw</bpmn:outgoing>
    </bpmn:exclusiveGateway>
    <bpmn:sequenceFlow id="Flow_0ztg4mq" sourceRef="Activity_1ijk7i6" targetRef="Gateway_13vlylm" />
    <bpmn:endEvent id="End_approved">
      <bpmn:incoming>Flow_0kt470w</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_0kt470w" sourceRef="Gateway_13vlylm" targetRef="End_approved">
      <bpmn:conditionExpression xsi:type="bpmn:tFormalExpression">=approved = true</bpmn:conditionExpression>
    </bpmn:sequenceFlow>
    <bpmn:endEvent id="End_rejected">
      <bpmn:incoming>Flow_0e7fpjw</bpmn:incoming>
    </bpmn:endEvent>
    <bpmn:sequenceFlow id="Flow_0e7fpjw" sourceRef="Gateway_13vlylm" targetRef="End_rejected" />
    <bpmn:textAnnotation id="TextAnnotation_0msudo5">
      <bpmn:text>Approved result</bpmn:text>
    </bpmn:textAnnotation>
    <bpmn:association id="Association_1s5cojk" associationDirection="None" sourceRef="End_approved" targetRef="TextAnnotation_0msudo5" />
    <bpmn:textAnnotation id="TextAnnotation_1cz23vb">
      <bpmn:text>Rejected result</bpmn:text>
    </bpmn:textAnnotation>
    <bpmn:association id="Association_1eq3bkz" associationDirection="None" sourceRef="End_rejected" targetRef="TextAnnotation_1cz23vb" />
  </bpmn:process>
  <bpmndi:BPMNDiagram id="BPMNDiagram_1">
    <bpmndi:BPMNPlane id="BPMNPlane_1" bpmnElement="Process_04iiy32">
      <bpmndi:BPMNShape id="StartEvent_1_di" bpmnElement="StartEvent">
        <dc:Bounds x="182" y="162" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Activity_0ceqnvb_di" bpmnElement="Activity_1ijk7i6">
        <dc:Bounds x="260" y="140" width="100" height="80" />
        <bpmndi:BPMNLabel />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Gateway_13vlylm_di" bpmnElement="Gateway_13vlylm" isMarkerVisible="true">
        <dc:Bounds x="395" y="155" width="50" height="50" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_0r2mvop_di" bpmnElement="End_approved">
        <dc:Bounds x="472" y="102" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="Event_139wrtk_di" bpmnElement="End_rejected">
        <dc:Bounds x="472" y="222" width="36" height="36" />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNEdge id="Association_1eq3bkz_di" bpmnElement="Association_1eq3bkz">
        <di:waypoint x="490" y="258" />
        <di:waypoint x="490" y="280" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Association_1s5cojk_di" bpmnElement="Association_1s5cojk">
        <di:waypoint x="490" y="102" />
        <di:waypoint x="490" y="80" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0nvvwuq_di" bpmnElement="Flow_0nvvwuq">
        <di:waypoint x="218" y="180" />
        <di:waypoint x="260" y="180" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0ztg4mq_di" bpmnElement="Flow_0ztg4mq">
        <di:waypoint x="360" y="180" />
        <di:waypoint x="395" y="180" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0kt470w_di" bpmnElement="Flow_0kt470w">
        <di:waypoint x="420" y="155" />
        <di:waypoint x="420" y="120" />
        <di:waypoint x="472" y="120" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNEdge id="Flow_0e7fpjw_di" bpmnElement="Flow_0e7fpjw">
        <di:waypoint x="420" y="205" />
        <di:waypoint x="420" y="240" />
        <di:waypoint x="472" y="240" />
      </bpmndi:BPMNEdge>
      <bpmndi:BPMNShape id="TextAnnotation_1cz23vb_di" bpmnElement="TextAnnotation_1cz23vb">
        <dc:Bounds x="440" y="280" width="100" height="30" />
        <bpmndi:BPMNLabel />
      </bpmndi:BPMNShape>
      <bpmndi:BPMNShape id="TextAnnotation_0msudo5_di" bpmnElement="TextAnnotation_0msudo5">
        <dc:Bounds x="440" y="50" width="100" height="30" />
        <bpmndi:BPMNLabel />
      </bpmndi:BPMNShape>
    </bpmndi:BPMNPlane>
  </bpmndi:BPMNDiagram>
</bpmn:definitions>

DMN Model

DMN XML
<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="https://www.omg.org/spec/DMN/20191111/MODEL/" xmlns:dmndi="https://www.omg.org/spec/DMN/20191111/DMNDI/" xmlns:dc="http://www.omg.org/spec/DMN/20180521/DC/" xmlns:di="http://www.omg.org/spec/DMN/20180521/DI/" id="allowAge_model" name="AllowAge" namespace="https://quantumdmn.com/definitions/allowAge_model">
<inputData id="inputData_a287e529-0027-4fae-af56-2b2ea3066614" name="age">
  <variable id="inputData_a287e529-0027-4fae-af56-2b2ea3066614_var" name="age" typeRef="number" />
</inputData>
<decision id="decision_05729af0-1ffa-4ae2-9624-788060219ba3" name="AllowAgeDecision">
  <variable id="decision_05729af0-1ffa-4ae2-9624-788060219ba3_var" name="AllowAgeDecision" typeRef="boolean" />
  <informationRequirement>
    <requiredInput href="#inputData_a287e529-0027-4fae-af56-2b2ea3066614"/>
  </informationRequirement>
  <knowledgeRequirement>
    <requiredKnowledge href="#bkm_cff4dcd0-6558-4765-904f-de68131e25f4" />
  </knowledgeRequirement>
  <invocation id="invocation_a8c298f7-9dc7-4cf0-9633-81aa3c614e59">
    <literalExpression>
      <text>allowAgeFunc</text>
    </literalExpression>
    <binding>
      <parameter name="age" />
      <literalExpression>
        <text>age</text>
      </literalExpression>
    </binding>
  </invocation>
</decision>
<businessKnowledgeModel id="bkm_cff4dcd0-6558-4765-904f-de68131e25f4" name="allowAgeFunc">
  <variable id="bkm_cff4dcd0-6558-4765-904f-de68131e25f4_var" name="allowAgeFunc" typeRef="boolean" />
  <encapsulatedLogic>
    <formalParameter name="age" typeRef="number" />
    <decisionTable id="dt_9955ef92-444d-45c2-bdc2-bf5811ccdbf7" hitPolicy="FIRST">
      <input id="input_09355653-e571-45e9-820c-5c77707717a5" label="Age">
        <inputExpression typeRef="number">
          <text>age</text>
        </inputExpression>
      </input>
      <output id="output_3738b3ef-ce3c-4a0b-aa99-39c77a28ffe5" label="Output" name="result" typeRef="boolean" />
      <rule id="rule_4d90c301-bea8-48ed-9c7f-4393df59d687">
        <inputEntry>
          <text>&gt;=25</text>
        </inputEntry>
        <outputEntry>
          <text>true</text>
        </outputEntry>
      </rule>
      <rule id="rule_ab2e4801-3b06-4b7e-92d6-31fc01a5f94d">
        <inputEntry>
          <text>-</text>
        </inputEntry>
        <outputEntry>
          <text>false</text>
        </outputEntry>
      </rule>
    </decisionTable>
  </encapsulatedLogic>
</businessKnowledgeModel>
<dmndi:DMNDI>
  <dmndi:DMNDiagram id="DMNDiagram_1">
    <dmndi:DMNShape id="dmnshape-decision_05729af0-1ffa-4ae2-9624-788060219ba3" dmnElementRef="decision_05729af0-1ffa-4ae2-9624-788060219ba3">
      <dc:Bounds x="73.91111111111114" y="175.61909722222222" width="100" height="80"/>
      <dmndi:DMNLabel/>
    </dmndi:DMNShape>
    <dmndi:DMNShape id="dmnshape-inputData_a287e529-0027-4fae-af56-2b2ea3066614" dmnElementRef="inputData_a287e529-0027-4fae-af56-2b2ea3066614">
      <dc:Bounds x="119.32222222222225" y="50.55243055555555" width="100" height="80"/>
      <dmndi:DMNLabel/>
    </dmndi:DMNShape>
    <dmndi:DMNShape id="dmnshape-bkm_cff4dcd0-6558-4765-904f-de68131e25f4" dmnElementRef="bkm_cff4dcd0-6558-4765-904f-de68131e25f4">
      <dc:Bounds x="-62.32222222222219" y="55.01909722222222" width="100" height="80"/>
      <dmndi:DMNLabel/>
    </dmndi:DMNShape>
    <dmndi:DMNEdge id="dmnedge-edge_inputData_a287e529-0027-4fae-af56-2b2ea3066614_decision_05729af0-1ffa-4ae2-9624-788060219ba3" dmnElementRef="edge_inputData_a287e529-0027-4fae-af56-2b2ea3066614_decision_05729af0-1ffa-4ae2-9624-788060219ba3">
      <di:waypoint x="169.32222222222225" y="90.55243055555556"/>
      <di:waypoint x="123.91111111111114" y="215.61909722222222"/>
    </dmndi:DMNEdge>
    <dmndi:DMNEdge id="dmnedge-edge_bkm_cff4dcd0-6558-4765-904f-de68131e25f4_decision_05729af0-1ffa-4ae2-9624-788060219ba3" dmnElementRef="edge_bkm_cff4dcd0-6558-4765-904f-de68131e25f4_decision_05729af0-1ffa-4ae2-9624-788060219ba3">
      <di:waypoint x="-12.322222222222187" y="95.01909722222223"/>
      <di:waypoint x="123.91111111111114" y="215.61909722222222"/>
    </dmndi:DMNEdge>
  </dmndi:DMNDiagram>
</dmndi:DMNDI>
</definitions>

Key configuration points:

  • Type: quantumdmn-decision (this matches our worker's handler).
  • Headers: We use a custom header xmlDefinitionID to tell the worker which decision to evaluate.
  • Input Mapping: We map process variables (like process_age) to the decision inputs (like age).

2. The Java Worker​

The worker uses the zeebe-client-java to connect to Camunda and the com.quantumdmn:dmn-java-client to talk to QuantumDMN.

First, add the dependencies to your pom.xml:

<dependency>
    <groupId>io.camunda</groupId>
    <artifactId>zeebe-client-java</artifactId>
    <version>8.5.0</version>
</dependency>
<dependency>
    <groupId>com.quantumdmn</groupId>
    <artifactId>dmn-java-client</artifactId>
    <version>1.1.0</version>
</dependency>

Then, implement the JobHandler:

public class QuantumDmnWorker implements JobHandler {
    private final DmnEngine dmnEngine;

    public QuantumDmnWorker() {
        // Initialize with Zitadel Service Account for SaaS
        Supplier<String> tokenProvider = new ZitadelTokenProvider(
            "path/to/key.json", 
            "https://auth.quantumdmn.com", 
            "your-zitadel-project-id"
        );

        DmnService service = new DmnService("https://api.quantumdmn.com", tokenProvider);
        this.dmnEngine = new DmnEngine(service, "your-project-id");
    }

    @Override
    public void handle(JobClient client, ActivatedJob job) {
        String decisionId = job.getCustomHeaders().get("xmlDefinitionID");
        String decisionName = job.getCustomHeaders().get("decisionName");
        
        // Evaluate the Decision
        Map<String, EvaluationResult> results = dmnEngine.evaluate(decisionId, job.getVariablesAsMap());
        EvaluationResult result = results.get(decisionName);

        // Complete the job with the result
        client.newCompleteCommand(job.getKey())
            .variable("decisionResult", result.getValue().getRawValue())
            .send()
            .join();
    }
}

3. Running the Worker​

The main application simply connects to Zeebe and registers the worker:

public static void main(String[] args) {
    try (ZeebeClient client = ZeebeClient.newClientBuilder()
            .gatewayAddress("127.0.0.1:26500") 
            .usePlaintext() 
            .build()) {
        
        client.newWorker()
            .jobType("quantumdmn-decision")
            .handler(new QuantumDmnWorker())
            .open();

        // Keep running...
        new Scanner(System.in).nextLine();
    }
}

Now, let's fire it up!

mvn exec:java

Or, if you prefer to build a standalone JAR:

mvn package
java -jar target/camunda-integration-worker-1.0.0-SNAPSHOT.jar

Why This Matters​

By offloading the decision logic to QuantumDMN, you gain:

  1. Separation of Concerns: Your process flow remains clean, unrelated to complex business rules.
  2. Power: You can use the full power of FEEL and DMN 1.5. Feel like defining a recursive function to calculate a loan amortization schedule? Go ahead!
  3. Auditability: Every decision execution in QuantumDMN is recorded with full trace details, showing exactly why a decision was made.

Try it Yourself​

Download the complete example from GitHub, configure your API tokens, and see how easy it is to upgrade your Camunda 8 processes with enterprise-grade decisioning.