Decision Tables

The World’s Most Famous Decision Modelling Technique

Example 1: Bring a Coat: DRD

DMN’s decision tables are unambiguous: automatic interpretation and execution is possible
Inputs are always combined with the and operator!
- Their entry expressions may specify or (comma separated) to match any of the values in a single rule
- To express an or within a rule, use additional rule(s)
Rules cannot be split further, they are the smallest unit of logic after an expression
Decision logic is declarative: it describes what, but not how and order of evaluation (rules and inputs) should not matter

The decision table’s Hit Policy determines how the rules are matched against the input values
Hit policies are either single-hit or multiple-hit
- Single: matches at most one result
- Multiple: matches potentially multiple rules and optionally aggregates them