camunda-dmn

name

camunda-dmn

description

Use this skill to author and validate DMN (Decision Model and Notation) decisions for Camunda 8 — decision tables and literal expressions inside a Decision Requirements Diagram (DRD). Use for: creating or editing `.dmn` files, picking the right hit policy, wiring a business rule task in BPMN to a DMN decision, validating decisions structurally (`npx dmnlint`) and behaviourally (CPT preferred, deploy fallback). Do not use for: writing FEEL syntax in detail (use camunda-feel), modelling the BPMN around a business rule task (use camunda-bpmn), authoring CPT test scenarios (use camunda-process-test). **Workflow skill** — author the decision, lint it, run it.

Camunda DMN

Author executable DMN 1.3 decisions for Camunda 8.8+. A .dmn file holds one Decision Requirements Diagram with one or more decisions; each decision is either a decision table or a literal expression. A BPMN business rule task references a decision by ID and gets the result back as a process variable.

Cross-References

• camunda-bpmn: Business rule task wiring (<zeebe:calledDecision decisionId="..." resultVariable="..."/>)
• camunda-feel: FEEL syntax inside input expressions, output entries, literal expressions
• camunda-process-test: Preferred behaviour validation — CPT exercises the decision via the calling BPMN
• camunda-process-mgmt: Fallback behaviour validation — deploy and run on a cluster (prefer local c8run)

Authoring

A DMN file declares the DMN 1.3 namespace and wraps one or more <decision> elements:

<definitions xmlns="https://www.omg.org/spec/DMN/20191111/MODEL/"
             id="DinnerDecisions" name="Dinner Decisions"
             namespace="http://camunda.org/schema/1.0/dmn">
  <decision id="dish" name="Dish">
    <decisionTable id="decisionTable_dish" hitPolicy="UNIQUE">
      <!-- inputs, outputs, rules -->
    </decisionTable>
  </decision>
</definitions>

The default namespace and the namespace="http://camunda.org/schema/1.0/dmn" attribute are mandatory.

A decision contains either a <decisionTable> (inputs / outputs / rules + hit policy) or a <literalExpression> (single FEEL expression — useful for combining upstream decisions). Multi-decision files link decisions with <informationRequirement><requiredDecision href="#upstream"/></informationRequirement>; Camunda evaluates only the root decision referenced from BPMN and pulls in required decisions transparently.

See references/decision-tables.md for the full XML of input/output clauses, unary-test grammar, worked examples per hit policy, COLLECT aggregators, type table, and DRG linking.

ID and naming rules

• Decision id, output name, decision-table column names: alphanumeric + _ only. No whitespace, no - (which is a FEEL operator), no other special characters. A violation silently breaks BPMN references — the resolved value is null at runtime.
• name attributes (Decision, InputData, BusinessKnowledgeModel, KnowledgeSource, DecisionService): any string. dmnlint flags missing name — set one even when id already conveys intent.
• String output entries must be quoted. "HIGH" is a string literal; bare HIGH parses as a variable reference and evaluates to null — no parse error, no lint warning.

Hit policies (Camunda-supported set)

Set on the decisionTable element (default UNIQUE). Camunda 8 supports five; the DMN spec defines more — PRIORITY and OUTPUT ORDER are not supported.

Hit policy	Result	Behaviour
UNIQUE	single	Exactly one rule must match; multi-match = runtime error.
ANY	single	Multiple may match, must all produce the same output; otherwise runtime error.
FIRST	single	Top-to-bottom; first match wins.
RULE ORDER	list	All matching rules' outputs, in rule order.
COLLECT	list / scalar	All matches in arbitrary order. With aggregation="SUM" | "MIN" | "MAX" | "COUNT", collapses to a single value.

Default to UNIQUE. Use FIRST for hard-then-soft semantics (e.g. "blocklist first, then accept rules"). Use COLLECT when a list output is genuinely the goal. See references/decision-tables.md for worked examples per policy.

Wiring the BPMN side

<bpmn:businessRuleTask id="ApplyDiscount" name="Apply discount">
  <bpmn:extensionElements>
    <zeebe:calledDecision decisionId="discount" resultVariable="discountPercent"/>
  </bpmn:extensionElements>
</bpmn:businessRuleTask>

decisionId matches the DMN decision id. resultVariable receives the result — single-result for UNIQUE/ANY/FIRST, list for RULE ORDER/COLLECT (or scalar with aggregator).

resultVariable overwrites. If the name matches an existing input variable, the input is clobbered — pick a distinct name (e.g. discountPercent not customer) so downstream activities can still read the input.

<zeebe:calledDecision> also accepts bindingType — latest (default), deployment, versionTag. See camunda-bpmn for the binding-type table; deployment is the right choice when BPMN and DMN are co-deployed.

FEEL inside DMN

DMN uses FEEL in inputExpression, inputEntry (unary tests), outputEntry, and literalExpression. Unlike BPMN, no = prefix — every text element is parsed as FEEL.

Input entries use the unary tests subset: the input value is implicit, < 5 means ? < 5, comma-separated literals are OR, comma-separated comparisons are AND, ranges are [1..10] / (1..10), not(...) negates, - matches anything.

See references/feel-in-dmn.md for the unary-test grammar, what you cannot do in a unary test, variable scope across linked decisions, and DMN-specific FEEL features.

Validation

Two layers — run both before declaring a file done.

1. Structural lint. A DMN edit is not structurally done until npx dmnlint reports zero issues.

[ -f .dmnlintrc ] || echo '{ "extends": "dmnlint:recommended" }' > .dmnlintrc
npx --yes dmnlint path/to/decision.dmn

For directory-wide work, discover .dmn files recursively first (skip .git, node_modules, target, build, .gradle, .mvn, .idea, .settings, .snapshots), then lint each discovered file. Keep a fix loop open: lint → targeted XML edits → re-lint until the set is clean.

Common rules: label-required (add a name), no-duplicate-requirements (drop the duplicate informationRequirement edge). See references/dmnlint.md for the full rule → fix mapping.

2. Behaviour validation by execution. dmnlint does not understand FEEL, hit-policy correctness, or type matches. Run the decision:

• Preferred — write or extend a CPT scenario that exercises each UNIQUE partition / FIRST cascade / COLLECT path. See camunda-process-test.
• Fallback — deploy c8ctl deploy decision.dmn process.bpmn --profile=local and start an instance with c8ctl await pi --id MyProcess --variables '{...}' --profile=local. Incidents surface as EXTRACT_VALUE_ERROR (FEEL problem) or DECISION_EVALUATION_FAILED (hit-policy violation). See camunda-process-mgmt.

A green BPMN-completes test only proves the decision didn't fail — not that the right rules fired. For behavioural correctness assertions (assertThatDecision, rule-ordinal matching per hit policy, DRG coverage), see references/testing-decisions.md.

References

• decision-tables.md — input/output clause shapes, unary-test forms, worked examples per hit policy, decision-level <variable> rules, type table, pitfalls
• feel-in-dmn.md — FEEL contexts in DMN, unary-tests vs full FEEL, scope across linked decisions
• dmnlint.md — dmnlint:recommended rules, rule → fix mapping, common pitfalls beyond what the linter catches
• testing-decisions.md — assertThatDecision, rule-ordinal matching, strategy by hit policy, DRG coverage, mock-vs-test