Database Systems 6th Edition by Ramez Elmasri, Shamkant B. Navathe

Exercise 1

Figure 20.2

Figure 20.3
-Change transaction T₂ in Figure 20.2b to read:
read_item(X);
X:= X+M;
if X > 90 then exit
else write_item(X);
Discuss the final result of the different schedules in Figure 20.3 (a) and (b), where M = 2 and N = 2, with respect to the following questions. Does adding the above condition change the final outcome? Does the outcome obey the implied consistency rule (that the capacity of X is 90)?