DMN: Decision Model and Notation
Stop burying business rules in code. Decision tables that business analysts can read, auditors can verify, and systems can execute.
The Hidden Decision Problem
Your BPMN diagram shows "Approve Loan" as a single gateway. But the actual decision involves 47 business rules across 12 criteria. Where do those rules live? In someone's head? In nested if-statements? In a spreadsheet from 2019?
What is DMN?
Decision Model and Notation (DMN) is an OMG standard for modeling business decisions. While BPMN shows when decisions happen, DMN showshow decisions are made.
Think of it this way: BPMN is the train track. DMN is the logic that decides which platform the train stops at.
BPMN (Process)
"When do we make a decision?"
Submit → Review → Gateway: Approved? → ...DMN (Decision)
"How do we make the decision?"
IF credit ≥ 700 AND debt < 40% → ApproveDecision Tables
The core of DMN. A table where each row is a business rule. Columns are inputs and outputs. No code required.
Loan Approval Decision
| # | Credit Score | Debt-to-Income | Employment Years | Decision |
|---|---|---|---|---|
| 1 | ≥ 750 | < 30% | ≥ 2 | Auto Approve |
| 2 | 700-749 | < 40% | ≥ 1 | Standard Review |
| 3 | 650-699 | < 50% | Any | Manual Review |
| 4 | < 650 | Any | Any | Decline |
| 5 | Any | ≥ 50% | Any | Decline |
Hit Policy
What happens when multiple rules match? Unique (only one), First (top wins), Collect (all matches).
Completeness
Does the table cover all possible input combinations? DMN tools can verify this automatically.
Consistency
Are there contradictory rules? Same inputs should never produce different outputs.
DMN Resources
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