Q3)Describe how a non-recoverable situation could arise if write locks are released after the last operation of a transaction but before its commitment. Q4) The executions of transactions are strict if read and write operations on an object are delayed until all transactions that previously wrote that object have either committed or aborted. Explain how the locking rules in Figure 16.16 ensure strict executions. 696 CHAPTER 16 TRANSACTIONS AND CONCURRENCY CONTROL Figure 16.16 Use of locks in strict two-phase locking 1. When an operation accesses an object within a transaction: (a) If the object is not already locked, it is locked and the operation proceeds. (b) If the object has a conflicting lock set by another transaction, the transaction must wait until it is unlocked. (c) If the object has a non-conflicting lock set by another transaction, the lock is shared and the operation proceeds. (d) If the object has already been locked in the same transaction, the lock will be promoted if necessary and the operation proceeds. (Where promotion is prevented by a conflicting lock, rule b is used.) 2. When a transaction is committed or aborted, the server unlocks all objects it