System Interface $S^{0}I$

To be able to make this task more concrete one has to make some assumptions about the wanted properties of the system interface $S^{0}I$. There have to be at least some keys 'A', 'B', 'C' which can be pressed. Furthermore there should be at least one door which is usually closed but can become open if the right electronic key has been entered. Properties are static in the sense that they represent some perceivable qualities during a certain time interval.