Tree Protocol B 1.Only exclusive locks are allowed. 2.The first lock by 7;may be on any data item.Subsequently,a data Q can be locked by Ti only if the parent of Q is currently locked by Ti. 3.Data items may be unlocked at any time. 4.A data item that has been locked and unlocked by T;cannot subsequently be relocked by T; Database System Concepts -5th Edition,Oct 5,2006 16.17 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 16.17 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 Tree Protocol 1. Only exclusive locks are allowed. 2. The first lock by Ti may be on any data item. Subsequently, a data Q can be locked by Ti only if the parent of Q is currently locked by Ti . 3. Data items may be unlocked at any time. 4. A data item that has been locked and unlocked by Ti cannot subsequently be relocked by Ti