Preconditions

You can pretest data before using it with a decision table.

Preconditions give you a way to test data to determine whether it can be checked by a decision table. If the data from an application that calls a decision table does not satisfy the preconditions of the table, the rules in the table are not executed.

You can also use preconditions to modify incoming data, and declare variables for a decision table.

The preconditions of a decision table are managed outside the decision table, typically in a separate dialog that you access from the decision table. You state preconditions as rules, for example:

definitions
   set ‘wealthy customer’ to a customer
      where the average monthly balance of this customer 
                                      is more than $1 000 000
if
   the state of residence of ‘wealthy customer’ is NY

These preconditions start by defining the variable wealthy customer. The preconditions then limit the scope of the rules in the decision table to customers who have an average monthly balance of $1 million, and reside in the state of New York.

The preconditions are tested before each rule in a table is executed. If an application presents data that passes the preconditions of a decision table, the data is tested by the preconditions before each rule in the decision table is executed. For example, if a table contains 10 rules, the preconditions can be tested 10 times.