More about Decision Table rules
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If you have in advance a Microsoft Excel spreadsheet in XLS file format that contains useful starting information for a decision table rule, you can incorporate (or "harvest") the XLS file and the information it contains directly into the decision table rule. See About the Rule from File wizard.
This feature lets people with no access to Process Commander to record their decision rules using a familiar software program.
In an activity, to evaluate a decision table rule and derive a value, your application can:
R-9272 In an activity, call the method Property-Map-DecisionTable method. As parameters, enter the target property name and the name of the decision table rule.
In an activity, call the standard function named DecisionTable.ObtainValue to evaluate a decision table rule. Use the syntax:
Lib(Pega-RULES:DecisionTable).ObtainValue(this, myStepPage, "decisiontablename")
Process Commander does not limit the
number of rows in a decision table rule. However, as a best practice to
avoid slow performance when updating the form and also avoid the Java
64KB code maximum, limit your decision table rules to no more than 300 to
500 rows. MARTT 6/21/07 clinic
The standard activity named @baseclass.DecisionTableLookup also evaluates a decision table. (This approach is deprecated.) MARIK 1/22/04
When you save a decision table rule, the system converts the rule to Java source code. As a learning or debugging aid, you can review this Java code.
C-1665Click the Show Java toolbar button (
) to see the system-generated
Java code that implements the decision table rule. The window presents a
read-only preview of the Java that implements this rule instance. This
Java code is not identical to the Java that executes at runtime, which
includes Java code inlined from other rule instances and reflects rules
in the requestor's RuleSet list. R-9569
When a Declare Expression rule has Result of decision
table for the Set Property To field, special
processing occurs at runtime when a property referenced in the decision
table rule 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
Pega Developer Network article 
PRKB-20805 Troubleshooting:
Declarative Expression does not execute when a decision rule provides no
return value.B-18749
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.