Kenneth Rosen Edition 7 Exercise 1.3 Question 57 (Page No. 36)

Question

The following sentence is taken from the specification of a telephone system: “If the directory database is opened,then the monitor is put in a closed state, if the system is not in its initial state.” This specification is hard to understand because it involves two conditional statements. Find an equivalent, easier to understand specification that involves disjunctions and negations but not conditional statements.

Answer 1

Assume, 

D: The directory database is opened. 

S: The system is in its initial state. 

C:The monitor is put in a closed state. 

Given specification is, “If the directory database is opened, then the monitor is put in a closed state, if the system is not in its initial state.”  

translate into logic,

(D$\wedge\neg$S)$\rightarrow$C $\equiv$ ($\neg$D)$\vee$S$\vee$C

Hence, easier to understand specifications is, Either "The directory database is not opened" or "The system is in its initial state" or "The monitor is put in a closed state".