The timestamps of the transactions determine the serializability order. Thus, if TS(Ti) < TS(Tj ), then the system must ensure that the produced schedule is equivalent to a serial schedule in which transaction Ti appears before transaction Tj . To implement this scheme, we associate with each data item Q two timestamp values: W-timestamp(Q) denotes the largest timestamp of any transaction that executed write(Q) successfully.

R-timestamp(Q) denotes the largest timestamp of any transaction that executed read(Q) successfully.