Transactions are units of program execution that access and update database items. A transaction must preserve database consistency. Concurrent transactions are allowed for increased throughput but can result in inconsistent views. Serializability ensures transactions appear to execute serially in some order. Conflict serializability compares transaction instruction orderings while view serializability compares transaction views. Concurrency control protocols enforce serializability without examining schedules after execution.

7. Transaction State (Cont.)

30. Precedence Graph for Schedule A T 3 T 4 T 1 T 2

34. End of Chapter

35. Schedule 2 -- A Serial Schedule in Which T 2 is Followed by T 1

36. Schedule 5 -- Schedule 3 After Swapping A Pair of Instructions

37. Schedule 6 -- A Serial Schedule That is Equivalent to Schedule 3

38. Schedule 7

39. Precedence Graph for (a) Schedule 1 and (b) Schedule 2

40. Illustration of Topological Sorting

41. Precedence Graph

42. fig. 15.21