多项选择题

A.No user or application has to remember or hide a password. 
B.It prevents everyone except a true DBA session from acquiring the READWRITE role. 
C.app.chk_readwrite is called whenever a user tries to access rows protected by the READONLY or READWRITE label. 
D.app.chk_readwrite is called by users or applications when they want to enable the READONLY or READWRITE role.