Techniques enable a user, such as a business analyst or a system administrator, to define business process rules that control the processing of transaction data by a computer application. A data structure is used to store business process rules. The data structure includes a condition portion and an execution portion of a rule. The user is able to identify one of multiple pre-defined functions to be included in the execution portion of a rule. At runtime, the computer system executing a computer application determines whether a condition portion of a rule is met, and in response to a determination that the condition portion is met, performs the identified pre-defined function included in the execution portion of the rule.