1. A method, in a data processing system, for authorizing information flows between elements of the data processing system, the method comprising: associating the elements of the data processing system with security data structures in a reference monitor; receiving an information flow request from a first element to authorize an information flow from the first element to a second element; retrieving a first security data structure associated with the first element; retrieving a second security data structure associated with the second element; and performing at least one set theory operation on the first security data structure and the second security data structure to determine if the information flow from the first element to the second element is to be authorized.