The determination of whether an event, such as a taxable event for a commercial transaction, has occurred uses an executable decision tree. The decision tree includes a number of test nodes that each include a comparison field and at least one allowed value. A data value associated with the comparison field is accessed and compared to the allowed values. If the comparison field equals an allowed value, execution proceeds to a child node, and if not, execution proceeds to a sibling node. The child and sibling nodes are either another test node, a result node, or an error node. Execution of the decision tree proceeds until a result node or an error node is reached.