In class exercises, October 28, 2014.

1) Draw the state machines that correspond to each individual process (slides 7, 8).

2) Now draw the combined state machine.  How many states?  How many transitions?

3) Sequential consistency:  
    The result of any execution is the same as if the (read and write)
    operations by all processes on the data store were executed in 
    some sequential order and the operations of each individual process 
    appear in this sequence in the order specified by its program.

Is this sequentially consistent?

   p1: W(x)a
   p2:       W(x)b
   p3:             R(x)b               R(x)a
   p4:                   R(x)b   R(x)a

How about this?

   p1: W(x)a
   p2:       W(x)b
   p3:             R(x)b               R(x)a
   p4:                   R(x)a   R(x)b

4) You access a web page on your phone.  You move to a different 
   location.  You access the same logical web page (but a different 
   copy - what kind of transparency is this?).
  
   What does "consistency" mean?