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Hit Policies

HitPolicy defines how the output of a decision is computed from the results of particular rules. The available policies are based on DMN Hit Policies with small changes in naming for increased clarity. Each HitPolicy comes with a dedicated evaluation method and return type.

When in doubt, we recommend using the Single policy as a default, as it is the most restrictive one. Alternatively, First is often the most intuitive and easy to reason about.

Each HitPolicy has a dedicated evaluation method, which returns a type specific to that policy.

HitPolicy.Single​

Allows for only one rule to be satisfied. Maps to the DMN Unique policy.

val single: DecisionTable[In, Out, HitPolicy.Single] = DecisionTable(rules, name, HitPolicy.Single)
single.evaluateSingle(in)

HitPolicy.Distinct​

Allows for multiple rules to be satisfied as long as they provide the same output. Maps to the DMN Any policy.

val distinct: DecisionTable[In, Out, HitPolicy.Distinct] = DecisionTable(rules, name, HitPolicy.Distinct)
distinct.evaluateDistinct(in)

HitPolicy.First​

The first satisfied rule defines the result, and others are ignored.

val first: DecisionTable[In, Out, HitPolicy.First] = DecisionTable(rules, name, HitPolicy.First)
first.evaluateFirst(in)

HitPolicy.Collect​

Outputs are collected into a list.

val collect: DecisionTable[In, Out, HitPolicy.Collect] = DecisionTable(rules, name, HitPolicy.Collect)
collect.evaluateCollect(in)

HitPolicy.CollectSum​

Outputs are combined together.

val collectSum: DecisionTable[In, Out, HitPolicy.CollectSum] = DecisionTable(rules, name, HitPolicy.CollectSum)
val merge: (Out[Value], Out[Value]) => Out[Value]            = ???
collectSum.evaluateSum(in)(merge)

HitPolicy.CollectMin​

The minimal output is returned.

val collectMin: DecisionTable[In, Out, HitPolicy.CollectMin] = DecisionTable(rules, name, HitPolicy.CollectMin)
given Ordering[Out[Value]]                                   = ???
collectMin.evaluateMin(in)

HitPolicy.CollectMax​

The maximal output is returned.

val collectMax: DecisionTable[In, Out, HitPolicy.CollectMax] = DecisionTable(rules, name, HitPolicy.CollectMax)
given Ordering[Out[Value]]                                   = ???
collectMax.evaluateMax(in)

HitPolicy.CollectCount​

The number of satisfied rules is returned.

val collectCount: DecisionTable[In, Out, HitPolicy.CollectCount] = DecisionTable(rules, name, HitPolicy.CollectCount)
collectCount.evaluateCount(in)