Database Reference
In-Depth Information
Each object is assumed to have lock and unlock operations. We should consider how the
two phases, of acquiring and releasing locks, can be implemented. In a centralized system
the transaction manager knows when locks on all the objects of a transaction have been
acquired and the operations done. The unlock operation can then be invoked on all the ob-
jects.
Phase 1: the commit manager requests and assembles the 'votes' for commit or abort of the
transaction from each participating node;
Phase 2: the commit manager decides to commit or abort, on the basis of the votes, and
propagates the decision to the participating nodes.
6.6 Grant and revoke
Some of the RDBMS provides security features to safe data stored in databases from un-
authorized viewing and damage. Appropriate rights are assigned to the users. These rights
are also called Privileges. Various objects like tables, views and sequences are created by
users, designer or DBA are controlled by these persons. If any user wants to access other
objects associated to another user, he/she has to take permission for such access. Giving
permission to another users is called Granting of Privileges. Privileges fall into two broad
categories:
System privileges permit the grantee to perform a general database function, like creating
new user accounts or connecting to the database.
Object privileges permit the grantee to perform specific actions on specific objects, such
as selecting, deleting or updating data from the STUDENT table. Some times, we assign
same privileges to number of users. Group of privilege definitions as a single named object
called a role.
In oracle data, control statements include the GRANT and REVOKE commands. Syntax
of GRANT command:
GRANT < Object privileges >
ON <objectname>
TO < username>
[ WITH GRANT OPTION ];
We have numbers of privileges and we can grant all or only specific privileges. These priv-
ileges are listed below:
ALTER: It is used give an access to a user to change the table definition or structure with
ALTER TABLE command
