DMN Elements

Decision Model and Notation (DMN) allows you to externalize business rules from BPMN processes into separate, version-controlled decision tables. Priostack supports DMN 1.3 with full FEEL expression evaluation.

Decision Table Structure

A decision table consists of:

Hit Policy — determines what happens when multiple rows match
Input columns — the variables being tested
Output columns — the values produced when a row matches
Rules (rows) — each row is a combination of input conditions and output values
Annotations — optional comments explaining each rule

Hit Policies

Policy	Code	Description
UNIQUE	U	Only one rule may match. If multiple rules match, evaluation throws an error. Use when rules are mutually exclusive.
FIRST	F	The first matching rule (in row order) is returned. Rules are evaluated top to bottom; once a match is found, evaluation stops.
RULE ORDER	R	All matching rules are returned in the order they appear in the table. Output is a list.
COLLECT	C	All matching rules are returned as a list (order not guaranteed). Can be combined with aggregators: `C+` (sum), `C<` (min), `C>` (max), `C#` (count).
ANY	A	Multiple rules may match, but all matching rules must produce the same output. Returns a single result.
OUTPUT ORDER	O	All matching rules are returned, ordered by the output values (ascending).

Example: Order Discount Decision

The following decision table determines the discount percentage based on customer tier and order amount:

Order Discount (Hit Policy: FIRST)
Rule	Customer Tier (Input)	Order Amount (Input)	Discount % (Output)
1	"gold"	> 500	15
2	"gold"	[100..500]	10
3	"silver"	> 200	8
4	"silver"	< 200	5
5	-	-	0

DMN XML for the above table

<?xml version="1.0" encoding="UTF-8"?>
<definitions xmlns="https://www.omg.org/spec/DMN/20191111/MODEL/"
             namespace="http://priostack.com"
             name="Order Discount"
             id="orderDiscount">
  <decision id="discount" name="Order Discount">
    <decisionTable id="decisionTable" hitPolicy="FIRST">
      <input id="input1" label="Customer Tier">
        <inputExpression id="inputExpr1" typeRef="string">
          <text>customerTier</text>
        </inputExpression>
      </input>
      <input id="input2" label="Order Amount">
        <inputExpression id="inputExpr2" typeRef="number">
          <text>orderAmount</text>
        </inputExpression>
      </input>
      <output id="output1" label="Discount %" name="discountPercent" typeRef="number" />
      <rule id="rule1">
        <inputEntry id="in1"><text>"gold"</text></inputEntry>
        <inputEntry id="in2"><text>> 500</text></inputEntry>
        <outputEntry id="out1"><text>15</text></outputEntry>
      </rule>
      <rule id="rule2">
        <inputEntry id="in3"><text>"gold"</text></inputEntry>
        <inputEntry id="in4"><text>[100..500]</text></inputEntry>
        <outputEntry id="out2"><text>10</text></outputEntry>
      </rule>
      <rule id="rule5">
        <inputEntry id="in9"><text></text></inputEntry>
        <inputEntry id="in10"><text></text></inputEntry>
        <outputEntry id="out5"><text>0</text></outputEntry>
      </rule>
    </decisionTable>
  </decision>
</definitions>

Input Expressions

Input expressions are FEEL expressions evaluated against the current process variables. The result is compared to each rule's input entry.

Input Entry Syntax	Meaning
`"gold"`	Exact string match
`> 500`	Greater than 500
`[100..500]`	Between 100 and 500 (inclusive)
`"gold", "platinum"`	One of these values
`not("cancelled")`	Any value except "cancelled"
(empty)	Matches any value (wildcard)

Referencing DMN from BPMN

Use a Business Rule Task in your BPMN to invoke a DMN decision. The decision output is written to a process variable.

<businessRuleTask id="applyDiscount" name="Calculate Discount">
  <extensionElements>
    <zeebe:calledDecision
      decisionId="discount"
      resultVariable="discountResult" />
  </extensionElements>
</businessRuleTask>

After execution, the variable discountResult will contain the output of the decision (e.g., {"discountPercent": 10}). You can then reference it in subsequent FEEL expressions as discountResult.discountPercent.

Tip: Use the DMN Editor to author decision tables visually. Deploy DMN files alongside BPMN files via the same POST /api/v1/process-definitions endpoint.

FEEL in Decision Conditions

Both input conditions and output expressions support full FEEL. This means you can use functions, context access, and list operations:

<!-- Input: check if status is in a list -->
<inputEntry><text>status in ["pending", "review"]</text></inputEntry>

<!-- Output: compute a value -->
<outputEntry><text>amount * 0.1</text></outputEntry>

<!-- Input: date comparison -->
<inputEntry><text>dueDate < today()</text></inputEntry>

For a complete FEEL reference, see the FEEL Reference page.