DMN
DMN 1.3 describes decisions: decision tables with hit policies, input data, and the requirement diagram showing what feeds what.
The important part is that it is executable in spirit. A DMN table with a Unique hit policy will tell you when two rules overlap, which a spreadsheet never will.
#What it is good at
Business rules with several inputs, maintained by non-engineers.
Decisions that will later run in a rules engine.
Anywhere overlapping rules have caused a production surprise.
#What it draws
Diagram | Syntax starts with |
|---|---|
Decision table | Inputs, outputs, rules, and a hit policy |
Hit policies | Unique, First, Priority, Any, Collect |
FEEL expressions | Ranges like [18..65], negations like not("UK"), comparisons |
Requirement diagram | Decisions, input data, knowledge sources and their links |
#A few things that catch people out
The hit policy changes behaviour when two rows match. It is not documentation.
FEEL is a real expression language; a cell can express a range, not just a value.
Keep the decision requirement diagram beside the tables; it is what explains the order.
#Related
Learn one properly. Borrow the rest when you need them.
