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Using Roles to Manage Database Access

When your databases has lots of tables, object privileges can become unwieldy and hard to manage. You can simplify the management of privileges with the use of a database object called a role. A role acts in two capacities in the database. First, the role can act as a focal point for grouping the privileges to execute certain tasks. Second, the role can act as a “virtual user” of a database, to which all the object privileges required to execute a certain job function can be granted, such as data entry, manager review, batch processing, and so on

Step 1:
  Design and Crate roles is a process that can happen outside the database. A role mechanism can be used to provide authorization. A single person or a group of people can be granted a role or a group of roles. One role can be granted in turn to other roles. By defining different types of roles, administrators can manage access privileges much more easily. You simply sit down and think to yourself, how many different purposes will users be accessing this application for? Once this step is complete, you can create the different roles required to manage the privileges needed for each job function. Let’s say people using the EMP table have two different job roles: those who can query the table and those who can add records to the table. The next step is to create roles that correspond to each activity. This architecture of using roles as a middle layer for granting privileges greatly simplifies administration of user privileges. Let’s take a look at how to create the appropriate roles:
Create role role_name;
Step 2 :  Granting Privileges to Roles
The next step is to grant object privileges to roles. You can accomplish this task using the same command as you would use to grant privileges directly to users—the grant command. The following code block demonstrates how to grant privileges to both our roles:
Grant select on emp to rpt_writer;
Revoking privileges from roles works the same way as it does for users. System privileges are granted and revoked with roles in the exact same way they are with users as well.
Step 3: Granting Roles to Users
Once a role is created and privileges are granted to it, the role can then be granted to users. This step is accomplished with the grant command. Let’s see an example of how this is done:
Grant rpt_writer to turner;
If a role already granted to a user is later granted another privilege, that additional privilege is available to the user immediately. The same statement can be made for privileges revoked from roles already granted to users, too.
Step 4:  Revoking and Dropping Roles
Finally, a role can be revoked by the role’s owner or by a privileged administrative user using the revoke statement, much like revoking privileges:
revoke rpt_writer from turner;
Roles can be deleted from the database using the drop role statement. When a role is dropped, the associated privileges are revoked from the users granted the role. The following code block shows how to eliminate roles from Oracle:
drop role rpt_writer;
Step 5: Modifying Roles if necessary
Let’s say that after we create our roles, we realize that changing records in the EMP table is serious business. To create an added safeguard against someone making a change to the EMP table in error, the DATA_CHANGER role can be altered to require a password by using the alter role identified by statement. Anyone wanting to modify data in EMP with the privileges given via the DATA_CHANGER role must first supply a password. Code for altering the role is shown in the following example:
Alter role data_changer
Identified by highly#secure;

Step 6: Defining User Default Roles
Now user TURNER can execute all the privileges given to him via the RPT_WRITER role, and user FORD can do the same with the privileges given from DATA_CHANGER. Or can he? Recall that we specified that DATA_CHANGER requires a password in order for the grantee to utilize its privileges. Let’s make a little change to FORD’s user ID so that this status will take effect:
alter user ford default role none;
You can use the following keywords in the alter user default role command to define default roles for users: all, all except rolename, and none. Note that users usually cannot issue alter user default role themselves to change their default roles—only a privileged user such as the DBA can do it for them.
Step 7: Enabling the Current Role
FORD knows he is supposed to be able to accomplish this task because he has the DATA_CHANGER role. Then he remembers that this role has a password on it. FORD can use the set role command to enable the DATA_CHANGER role in the following way:
set role data_changer identified by highly#secure;
Now FORD can make the change he needs to make:
SQL> insert into scott.emp (empno, ename, job)
  2  values (1234, ‘SMITHERS’,’MANAGER’);
You must already have been granted the roles that you name in the SET ROLE statement. Also, you can disable all roles with the SET ROLE NONE statement.
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