Explain Strict Two-Phase locking

A transaction T does not release any type of its exclusive (X) locks until that transaction commits or aborts. In this method no other transaction can access the item which is written by T unless the transaction T commits. This is a better method than the two discussed.

In 2PL, a transaction may not be capable to release its locks even after make use of it. The data item will stay locked until the transaction ends all the actions on all the data items. If each transaction in a schedule follows 2PL after that conflict serializability can be made sure. This is since if the schedule is not serializable, the precedence graph for schedule S contains transactions T1, T2 ..... Tn will have a cycle ... assume that a cycle consists of T1, T2 ..... Tn ,T1.  The meaning of this is that a lock operation by T2 is followed by an unlock operation by T1; A Lockoperation T3 is followed by an unlock operation by T2 ... and etc.  Though this is a contradiction of the assertion that T1 is by using two phase locking protocol. So the assumption that graph is having a cycle is wrong and therefore S is serializable.