Bev Littlewood Sarah Brocklehurst Norman E. Fenton P. Mellor Stella Page David Wright J. Dobson J. McDermid Dieter Gollmann Towards Operational Measures of Computer Security. 211-230 1993 2 Journal of Computer Security 2-3 db/journals/jcs/jcs2.html#LittlewoodBFMPWDMG93