Glenn S. Benson Ian F. Akyildiz William F. Appelbe A Formal Protection Model of Security in Centralized, Parallel, and Distributed Systems. 183-213 1990 8 ACM Trans. Comput. Syst. 3 http://doi.acm.org/10.1145/99926.99928 db/journals/tocs/tocs8.html#BensonAA90