DBMS Security and Authorization

It is a Data Control Language (DCL) command.

This statement in Oracle is a group of privileges that are collected together and granted to users.

Create, Revoke, Grant and Drop commands are parts of data definition language in Oracle.

This type of lock in Oracle locks the table allowing other user to only query but not insert, update or delete rows in table.

In database systems, the external level (or view level) provides a user-oriented view of data while hiding implementation details. When salary information is hidden from employees but accessible to directors, this is external level data hiding - different users see different views of the same data based on their access privileges. This abstraction layer separates how users see data from how it's physically stored.

When multiple users try to update the same record simultaneously, record locking prevents conflicts by ensuring only one transaction can modify the record at a time. This concurrency control mechanism prevents the lost update problem where two updates overwrite each other. Locking maintains data integrity and consistency in multi-user database environments.

The SQL statement to grant select, update privileges to the user RAKESH for the DEPT relation is
GRANT select, update on DEPT to USER1;

The two-phase locking protocols are:

1. Growing phase- Here transaction may obtain lock but not able to release any lock.
2. Shrinking phase- Here transaction may release lock but not able to obtain any lock.

A locked file can only be accessed by the single user or process that holds the lock. This exclusive access prevents other users from reading, modifying, or accessing the file until the lock is released. Locking is a fundamental mechanism for protecting data integrity when files are being used by multiple concurrent users or processes.

Locking prevents the lost update problem, which occurs when two transactions read the same data and then overwrite each other's updates. By locking data before updating, one transaction waits for the other to complete, ensuring updates are applied sequentially. Deadlock (A) is a potential problem with locking, not a solution. Uncommitted dependency (C) and inconsistent data (D) are other concurrency issues that locking addresses.

These tools are used to manage an Oracle distributed database system.
'Site autonomy' means each server participating in a distributed database is administered independently from all other databases.

An exclusive lock provides exclusive access to a resource, preventing other users or processes from sharing it. Only the lock holder can access the locked data. This contrasts with shared locks (read locks) that permit multiple concurrent readers. Exclusive locks are used for write operations to prevent concurrent modifications and maintain data integrity.