## Problem-23

Problem-23

Are these system specifications consistent?

“Whenever the system software is being upgraded, users cannot access the file system. If users can access the file system, then they can save new files. If users cannot save new files, then the system software is not being upgraded.”

Let the following statements be represented symbolically as shown:

u: “The software system is being upgraded.”
a: “Users can access the file system.”
s: “Users can save new files.”

Write each system specification symbolically.

a) “Whenever the system software is being upgraded, users cannot access the file system.”

b) “If users can access the file system, then they can save new files.”

c) “If users cannot save new files, then the system software is not being upgraded.”

d) Is the system consistent?

Solution

a) “Whenever the system software is being upgraded, users cannot access the file system.”

u→¬a

b) “If users can access the file system, then they can save new files.”

a→s

c) “If users cannot save new files, then the system software is not being upgraded.”

¬s→¬u

d) Is the system consistent?

Yes, for example making v false, a false, and s true makes it consistent.