Decision tree evaluation may be based on a known property identified on the Configuration tab, or on a parameter supplied in the Property-Map-DecisionTree method, or both.
If you leave the Property field blank, evaluation is always based on the parameter. If a parameter is supplied, the parameter value is used even when the Property field is not blank.
As an alternative to the Property-Map-DecisionTree method, you can use these standard functions to evaluate a decision tree:
@(Pega-RULES:DecisionTree).ObtainValue(tools, myStepPage, decisiontree, inputproperty)
@(Pega-RULES:DecisionTree).ObtainValue(tools, myStepPage, decisiontree, inputproperty, bAllowMissingProperties)
Decision tree rules can also be evaluated as part of a collection rule (Rule-Declare-Collection rule type).
See PDN article How to evaluate a decision tree and handle errors for an example.
You can create a decision tree by importing (or "harvesting) a specially formatted text file. This capability lets others not familiar with the Pega Platform create decision trees.
The number of nodes in a decision tree is not limited. However, as a best practice to avoid slow performance when updating the form and also avoid the Java 64 KB code maximum, limit your decision trees to no more than 300 to 500 rows.
Click Actions > View Java to view the generated Java of a rule. You can use the Java code to debug your application or to examine how rules are implemented.
When a Declare Expression rule has Result of decision tree for the Set Property To field, special processing occurs at runtime when a property referenced in the decision table is not present on the clipboard. Ordinarily such decision rules fail with an error message; in this case the Otherwise value is returned instead. For details, see PDN article Troubleshooting: Declarative Expression does not execute when a decision rule provides no return value.
Despite the class name, the Rule-Declare-DecisionTable rule type does not produce forward or backward chaining. Technically, it is not a declarative rule type.