the security mediator as specified by the rules operations that can be invoked include random falsification of data and aggregation the security mediator updates internal statistics such as the number of queries for the session and duration of the session it also updates the log files appropriately this last step is done in all cases whether or not there were errors most databases in place today were originally developed for internal use only the security mechanisms available in these systems are intended for access by only a known controllable observable and predominantly loyal internal user population rather than unknown unseen and potentially adversarial external user populations consequently while internal access control based on user discretion might be satisfactory external access control should support mandatory enforcement before an enterprise can comfortably share its data with other partners in a collaboration notice that the tables referred to in the rules do not have to be base relations they can be derived relations or views defined by arbitrary sql queries hence the set of rules collectively specifies a view based access control policy views in relational databases have long been considered ideal as the objects of access control because they have a higher degree of logical abstraction than physical data and hence enable content based or context based security as opposed to container based security provided in operating systems view based access control in relational databases was first introduced in ibm 39 s system r in which views expressed in sql are the objects of authorization it has been adopted by most commercial relational dbms 39 s however view based mandatory access control has not been in wide spread use because of the safety problem the safety question asks the following is there a.