Differentiate between strict two-phase and rigorous two-phase with conversion protocol

Ans:  Strict two-phase locking holds all its exclusive that is write locks until commit time, one time granted. When Rigorous two-phase locking is more restrictive as compared to standard 2PL in that it enforces the rule that no locks can be released through a transaction until after it commits or aborts. The former locks all its items previous to it starts thus once transaction starts, it is in its shrinking phase while latter does not unlock any of its items until after it terminates to the transaction is in its expanding phase till it ends.