Data structures for use in controlling access to data objects by users of a computer system or computing device are described. The data structures include an access control group data structure, a user access data structure, and a data object access data structure. The access control group data structure stores access control group data. The user access data structure stores user access data. The user access data relates to at least one entry in the access control group data structure. The data object access data structure stores data object access data, which relates to at least one entry in the access control group. Additional data structures described include an access control rule data structure and a characteristic method data structure.