Explanation: An external time counter cannot be used to implement a timestamp. System clock and a logical counter can be used.

Explanation: A logical counter is incremented after a new timestamp has been assigned everytime.

Explanation: W-timestamp(Q) denotes The largest timestamp of any transaction that can execute write(Q) successfully.

Explanation: R-timestamp(Q) denoted the largest timestamp of any transaction that can execute read(Q) successfully.

Explanation: A timestamp ordering protocol ensures that any conflicting read and write operations are executed in timestamp order.

Explanation: The timestamp ordering protocol generates schedules that are non-recoverable. But it can be extended to make the schedules recoverable.

Explanation: The Thomas write rule has a greater potential concurrency than the timestamp ordering protocol. This is because it is a modified version of the timestamp ordering protocol in which obsolete write operations can be ignored under certain circumstances.

Explanation: Thomas write rule protocol generates serializable schedules that no other protocol can generate.

Explanation: Suppose that transaction Ti issues read(Q). If TS(Ti ) < W-timestamp(Q), then Ti needs to read a value of Q that was already overwritten. Hence, the read operation is rejected, and Ti is rolled back.

Explanation: In timestamp ordering protocol, suppose that the transaction Ti issues write(Q) and TS(Ti)<W-timestamp(Q), then the value of Q that Ti is producing was needed previously, and the system assumed that the value would never be produced. Hence the system rejects the write(Q) operation and the transaction Ti rolls back.