Camunda 8 DMN vs Camunda 7 DMN – Key Differences

Decision Model and Notation (DMN) is a standards-based way to define, manage and automate business decisions that are part of your process automation solution. Both Camunda 7 and Camunda 8 support DMN, but there are important differences in how DMN is executed, modelled and integrated in the newer version.

🎯 1. Underlying Engine and Architecture

One of the most fundamental differences between Camunda 7 and Camunda 8 — and therefore for DMN — is the engine architecture:

  • Camunda 7 is built on the traditional Java-based process engine.

  • Camunda 8 uses the Zeebe engine, designed for cloud-native, scalable execution of both BPMN and DMN models.

This means that in Camunda 8, DMN execution is part of a distributed, horizontally scalable decision engine, whereas in Camunda 7 it runs in a monolithic embedded or server-based JVM. This foundational change influences performance and how decision models are deployed and scaled.

🧠 2. Expression Language Used in DMN

A key technical difference involves how expressions inside DMN tables are evaluated:

  • Camunda 7 uses JUEL (Java Unified Expression Language). This allows expressions to access Java objects and beans directly within decision logic.

  • Camunda 8 uses FEEL (Friendly Enough Expression Language), which is part of the DMN standard and works on JSON and simple data types without direct access to Java objects.

👉 This means you often need to rewrite or adjust decision logic when migrating DMN models from 7 to 8, especially if you relied on Java code inside DMN expressions.

📊 3. Supported Data Types and Variable Handling

Another area that affects decision tables is how data is stored and referenced:

  • Camunda 7 supports a wide range of data types including serialized Java objects.

  • Camunda 8 restricts variables to primitive types and JSON, which is essential for cloud scalability and consistent behaviour across distributed nodes.

This means you may need additional data mapping or transformation when passing complex objects into DMN decision tables in Camunda 8.

🔄 4. Decision Automation and Integration with BPMN

Camunda 8’s decision engine is designed to automatically trigger DMN models as part of BPMN processes, leveraging Zeebe’s execution model. This provides:

  • Better integration with workflows

  • Faster evaluation of decision logic at scale

  • A unified execution model that handles process and decision automation together

In Camunda 7, DMN tables can be executed from BPMN using the DMN task, but the runtime characteristics and performance differ since the engines operate differently.

🛠️ 5. Migration Considerations

When migrating from Camunda 7 to Camunda 8, decision tables need specific attention:

  • DMN models must be checked for syntax, expression compatibility, and logic adjustments to work with FEEL and the Camunda 8 DMN engine.

  • Tools like Camunda’s Migration Analyzer & Diagram Converter can help identify DMN elements that require manual modification.

This step is critical because mismatches in variable types or unsupported expressions can lead to incorrect decision outputs after migration.

📌 Summary: Core DMN Differences

AspectCamunda 7 DMNCamunda 8 DMN
EngineTraditional JVMZeebe cloud-native engine
Expression LanguageJUELFEEL
Data TypesJava objects & JSONPrimitive & JSON only
HostingEmbedded / ServerDistributed / cloud-oriented
MigrationManual updates often neededRequires conversion & testing

Final Thoughts

While the core concepts of decision modelling remain the same across Camunda 7 and Camunda 8 — both following the DMN standard — the most important differences lie in execution behaviour, expression language, data handling, and integration with a scalable workflow engine.

For teams upgrading from Camunda 7 to Camunda 8, DMN migration isn’t just a lift-and-shift — it often involves thoughtful refactoring of decision logic to align with FEEL expressions and cloud-ready data practices. With the right tooling and planning, however, you can unlock the performance and scalability benefits of Camunda 8’s modern DMN engine.

 

💼 Professional Support Available

If you are facing issues in real projects related to enterprise backend development or workflow automation, I provide paid consulting, production debugging, project support, and focused trainings.

Technologies covered include Java, Spring Boot, PL/SQL, CMS, Azure, and workflow automation (jBPM, Camunda BPM, RHPAM).

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