MARIA: Ay, but you must confine yourselfwithin the modest limits of order.
|--Twelfth Night, I, iii, 8–9.|
In 1976, Harrison, Ruzzo, and Ullman  proved that in the most general abstract case, the security of computer systems was undecidable and explored some of the limits of this result. In that same year, Jones, Lipton, and Snyder  presented a specific system in which security was not only decidable, but decidable in time linear with the size of the system. Minsky  suggested a third model to examine what made the general, abstract case undecidable but at least one specific case decidable. Sandhu  extended this model to examine the boundary even more closely.
These models explore the most basic ...