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Decision Table Hit Policy

The Hit Policy specifies the result of the Decision Table in cases of overlapping rules. The single character in a particular Decision Table cell indicates the table type and unambiguously reflects the decision logic.

Single Hit Policies:

  • Unique: no overlap is possible and all rules are disjoint; only a single rule can be matched (this is the default)
  • Any: there might be overlap, but all the matching rules show equal output entries for each output, so any match can be used
  • Priority: multiple rules can match, with different output entries; this policy returns the matching rule with the highest output priority
  • First: multiple (overlapping) rules can match, with different output entries; the first hit by rule order is returned

Multiple Hit Policies:

  • Output order: returns all hits in decreasing output priority order
  • Rule order: returns all hits in rule order
  • Collect: returns all hits in arbitrary order; an operator (‘+’, ‘<’, ‘>’, ‘#’) can be added to apply a simple function to the outputs

Collect operators are:

  • + (sum): the result of the Decision Table is the sum of all the distinct outputs
  • < (min): the result of the Decision Table is the smallest value of all the outputs
  • > (max): the result of the Decision Table is the largest value of all the outputs
  • # (count): the result of the Decision Table is the number of distinct outputs

Example of Unique Hit Policy

The 'Unique' Hit Policy is the most popular type for a Decision Table and all rules are disjoint.

Example of Priority Hit Policy

In a table with the 'Priority' Hit Policy, multiple rules can match, with different output entries. This policy returns the matching rule with the highest output priority.

Note: The list of allowable values is used to define the output priority. Here, the allowable values are listed as INELIGIBLE and ELIGIBLE; INELIGIBLE is defined as having a higher priority than ELIGIBLE.

One possible simulation result might resemble this:

The matching rules are highlighted, but the output from rule 2 is chosen because INELIGIBLE has higher priority than ELIGIBLE.

Example of Collection-Sum Hit Policy

For a Decision Table with the 'Collect-Sum' (C+) Hit Policy, the result of the Decision Table is the sum of all the distinct outputs.

In this example, the output Partial Score is calculated as 43 + 45 + 45 = 133