DBMS

DBMS:
A DBMS is a set of programs that is used to store and manipulation data. Manipulation
of data include the following:

1. Adding new data, for example adding details of new student.
2. Deleting unwanted data, for example deleting the details of students who have completed course.
3. Changing existing data, for example modifying the fee paid by the student.

A DBMS provides various functions like data security, data integrity, data sharing, data concurrence, data independence, data recovery etc. 



Data sharing, concurrency and locking:


DBMS also allows data to be shared by two or more users. The same data can be accessed by multiple users at the same time – data concurrency. However when same data is being manipulated at the same time by multiple users certain problems arise. To avoid these problems, DBMS locks data that is being manipulated to avoid two users from modifying the same data at the same time. The locking mechanism is transparent and automatic. Neither we have to inform to DBMS about locking nor we need to know how and when DBMS is locking the data.


Data Security:


While DBMS allowing data to be shared, it also ensures that data in only accessed by authorized users. DBMS provides features needed to implement security at the enterprise level. By default, the data of a user cannot be accessed by other users unless the owner gives explicit permissions to other users to do so.



Data Integrity:


Maintaining integrity of the data is an import process. If data loses integrity, it becomes unusable and garbage. DBMS provides means to implement rules to maintain integrity of the data. Once we specify which rules are to be implemented, then DBMS can make sure that these rules are implemented always.
Three integrity rules – domain, entity and referential are always supported by DBMS.

Fault tolerance and recovery:


DBMS provides great deal of fault tolerance. They continue to run in spite of errors, if possible, allowing users to rectify the mistake in the mean time. DBMS also allows recovery in the event of failure. For instance, if data on the disk is completely lost due to disk failure then also data can be recovered to the point of failure if proper back up of the data is available.


DBMS supports a data access and manipulation language. The most widely used data access language for RDBMS (relational database management systems) is SQL. Apart from supporting a non-procedural language like SQL to access and manipulate data DBMS now a days also provides a procedural language for data processing. Oracle supports PL/SQL and SQL Server provides T-SQL.