What is activity of argument in boolean function and the norm of a function?

Question

1) I having problem understanding the concepts of activity of specific variable of a boolean function. For instance if we are given

F= (x1'x2)XOR(x3 v x4')x5 

what is the activity of x1 or x3 or combination of x4 and x5? I just want the procedure for calculating the activities. I couldn't find it anywhere?

So, could you please explain the approach for the given or any arbitrary function?

2)My second problem is how to calculate the norm of a boolean function? and what is the meaning of norm in boolean algebra?

for instance:

F= (x1 v x2) XOR x3(x4' v x5')x6'

Or any other fancy function. I googled a lot but couldn't find anything useful.

EDIT

activity questions

norm questions

And keys: 41)c 42)b 43)b 44)c 50)c 51)b 52)c

Answer 1

What do you mean by the "activity of a specific variable"?

Also, why do you expect a standard norm to be defined on a Boolean algebra? Do you have a norm on Boolean algebras that you're looking at? A norm tends to mean the same thing, just varying in how it's computed (i.e. satisfies the properties listed here).

If you can't find the definition of a norm on a Boolean algebra, maybe you can find your own that qualifies as a norm!