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e special views and stored procedures to restrict access to the contents of the database table . DBA and database systems can allow users with specific access privileges to grant access to other users.

Access control is mainly divided into discretionary access control and mandatory access control , role-based access control.
Discretionary Access Control (DAC) with access permission is subject , directly or indirectly, access to other body transfer , is one of the most common means of access control . Discretionary Access Control body can at will determine which users can access their resources, that the subject has the right to decide their own , a body can be selectively shared with other subjects of his resources. Discretionary Access Control One of the biggest problems is the principal's privileges is too large, it may inadvertently disclose information, but can not guard against Trojan horse attacks. In the mandatory access control (MAC) method, each data object is marked with a security classification , each user can be granted a level of a license . For any one object, and only those with legitimate users can access the license . Users can take advantage of discretionary access control to prevent other users on their own object of attacks , because the user can not directly change the mandatory access control attributes, mandatory access control provides an insurmountable , stronger security protection layer to prevent other users from accidental or intentional abuse of discretionary access control . Role-based access control (RBAC) is currently popular on the international advanced security access control method , and canceling it by assigning roles to complete the granting and revoking user permissions , and users based on their responsibilities and qualifications no longer be assigned to different roles . Thus, the entire access control process is divided into two parts, namely access is associated with the role , role and then associated with the user , enabling the user with access to the logic of separation , is now recognized to solve large-scale enterprise unified resource access control effective way .

2 ) User Identification and Authentication
Database system contains a large number of sensitive and confidential data , users must authenticate visiting . User identification and authentication [ 13 ] is a system to provide the most basic security measures . The method is provided by the system in a certain way so that users identify themselves by name or identity . Each user requirements into the system, be checked by the system , through the identification of the right to use machines have been provided after . Generally common user authentication methods are the following forms: password authentication ; digital certificate authentication ; smart card authentication and identification of personal characteristics . The four user authentication methods in all areas of life have different range of applications , authentication security is also different.

( 1 ) password authentication . This is a widely used authentication method . To ensure the security of the database , the user's password, and the password stored in encrypted form , and to periodically change the user 's password and password. Some systems store the password -way Hash value , even if the attacker is difficult to launch the ciphertext plaintext passwords .

( 2 ) digital certificates.