Exercise 18.2.1: Below are two transactions, described in terms of their effect on two database elements A and B, which we may assume are integers. Ti: READ(A, t); t:= t+ 2 ; WRITE(A ,t) ; READ(B, t); t:= t* 3 ; WRITE(B, t); T2: READ(B, s); s:=s*2; WRITE(B, s); READ(A, s); s:=s+3; WRITE(A. s); 896 CHAPTER 18. CONCURRENCY CONTROL We assume that, whatever consistency constraints there are on the database, these transactions preserve them in isolation. Note that A = B is not the consistency constraint. a) It turns out that both serial orders have the same effect on the database; that is, (Ti ,T2) and (T2,T i) are equivalent. Demonstrate this fact by showing the effect of the two transactions on an arbitrary initial database state. b) Give examples of a serializable schedule and a nonserializable schedule of the 12 actions above. c) How many serial schedules of the 12 actions are there?