DMN XML and Interoperability

Verdict reads DMN 1.3, 1.4 and 1.5, and writes 1.3 by default.

Writing the newest version it can read would be defensible and wrong: Camunda Modeler and every editor built on dmn-js read 1.3 only. A model no editor opens is not interoperable whatever the version number in it says.

verdict convert model.vdj --to xml --out model.dmn      # DMN 1.3, with a diagram
verdict convert model.vdj --to xml --dmn-version 1.5    # newest namespace, few readers
verdict convert model.vdj --to xml --no-diagram         # schema-valid, empty canvas

The reader is namespace-tolerant: it matches on local element names, so a document from a tool that declares DMN under an unexpected prefix, or mixes 1.3 and 1.4 namespaces, still loads.

Diagram interchange is generated

A DMN document without DMNDI is perfectly schema-valid and opens as an empty canvas in every dmn-js editor. Verdict therefore generates diagram interchange from the DRG whenever it writes XML: shapes laid out in dependency layers, edges for every requirement, translated into the positive quadrant so the diagram opens on its own content.

Coordinates are generated, never hand-maintained. If you change an example model’s shape, make diagrams regenerates them.

Three ways the XSD is stricter than the reader

These bit us once already, which is why make validate exists. Verdict’s own reader accepts all three; the schema — and therefore Camunda — does not.

1. tDefinitions admits foreign attributes only when namespaced. Verdict’s own metadata travels as verdict:version and verdict:conformanceLevel, never bare. version and conformanceLevel are not DMN attributes, and a bare one fails validation for the whole document.

<definitions xmlns="https://www.omg.org/spec/DMN/20191111/MODEL/"
             xmlns:verdict="https://github.com/frankbardon/verdict/schema/1.0"
             verdict:version="2.1.0"
             verdict:conformanceLevel="feel">

2. tDecision’s logic slot admits only DMN’s own expression substitution group. A foreign element there — an agentDecision, say — fails validation for the entire file. So an agent decision travels in <extensionElements> instead, positioned by tDMNElement’s sequence: immediately after <description>, before <question>.

<decision id="risk_tier" name="Risk Tier">
  <description>Assessed from the applicant's notes.</description>
  <extensionElements>
    <verdict:agentDecision>…</verdict:agentDecision>
  </extensionElements>
  <question>How risky is this applicant?</question>
  <variable name="RiskTier" typeRef="string"/>
  <informationRequirement>…</informationRequirement>
</decision>

A standard DMN tool that round-trips this model sees a typed extension element in a slot the schema explicitly reserves for extensions, and either preserves it or warns — rather than refusing the document.

3. tItemDefinition is an xsd:choice. A definition is either a constrained simple type or a structure — never both. Emitting typeRef and itemComponent together validates in Verdict’s reader and fails everywhere else.

Element order is fixed

description comes first in every element, because it comes from tDMNElement. In a decision the order is:

description → extensionElements → question → allowedAnswers → variable → requirements → logic

Getting this wrong is the most common hand-authoring mistake, and the error message from a validator points at the second element, not the misplaced one.

Verify it, do not assert it

“It parses in our reader” is not a claim about anyone else’s tool. Verdict validates against the real OMG schemas, vendored under pkg/dmn/xml/testdata/schema/:

make validate

OK   examples/content_moderation/content_moderation.dmn
OK   examples/loan_approval/loan_approval.dmn
OK   examples/pricing/pricing.dmn

The Go test suite runs the same validation (pkg/dmn/xml/schema_test.go) but skips when xmllint is absent, so the make target fails loudly instead — an interoperability check that silently skips silently rots. It covers both directions: the shipped examples as authored, and every example re-written through the writer, plus a model exported from Camunda.

The schemas are vendored rather than fetched. A validation gate that reaches omg.org is a gate nobody trusts after the third false alarm.

Conformance

Declaring level 2 is not decoration — the dialect gate rejects FEEL-only constructs at load time with VERDICT_LOAD_010, so a model that claims to be portable S-FEEL is held to it.

Java-bound and PMML function definitions are parsed and preserved through a round trip, but not executed: calling one returns null and reports VERDICT_LOAD_007 or VERDICT_LOAD_008 at load, and VERDICT_EVAL_011 when evaluated. A model that uses them loads and every other decision in it still runs.