DBMS

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Rahul Bansal

Finalist

35929 Points Joined September 2009

DATABASE MANAGEMENT SYSTEMS

(DBMS)

A database is a collection of logically related information.

Database Management is the task of maintaining databases so that information is readily available.

Management of database involves:

- Defining structures for data storage.

- Providing mechanism for data manipulation such as adding, editing, deleting, etc. the data

- Providing data security against unauthorized access.

The software required to perform the task of database management is called a Database Management System (DBMS).

In simple terms, A collection of programs required to store and retrieve data from a database is called a Database Management System.

The main objectives of any DBMS are to:

- Provide an efficient and convenient environment that is used to store in, and retrieve data from a database.

- Manage information about users who interact with the DBMS and the activities that these users can perform on the data.

DBMS controls the interaction between the database and application programs prepared by programmers on one hand and between the database and non-programming or ad hoc users on the other. It also provides mechanisms for maintaining the integrity of stored information, managing security and user access, backup and recovery procedures.

A DBMS can organize, process and present selected data elements from the database. This capability enables decision-makers to make special queries for searching database contents that are not available in regular reports. For example, a database may contain the net salary of all the employees of the organization. The regular report presents a list of the employees with their net pay, in the ascending order of names or pay. However, if it is desired to generate a list of employees drawing a salary in excess of Rs.5000 out of the total, the answer would be provided by posing a special query through the DBMS.

While maintaining a unified database they cater to the different requirements of these different users. This is made possible by the DBMS by providing two `views’ of the database i.e. a Physical view and a Logical view. The physical view deals with actual physical arrangement and location of data in the storage devices. The logical view or the user’s view is the representation of data in a form which is meaningful to the user. While there can be only one physical view of the database, there can be endless number of logical views, one specifically suitable for every individual user.

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Rahul Bansal

Finalist

35929 Points Joined September 2009

Functions of DBMS

A DBMS performs the following services:-

1. Transaction processing: A transaction is a sequence of database operations that represents a logical unit of work. In other words, it represents accessing a database record and updation, modification, deletion etc. thereof.

2. Concurrent Manager: A DBMS acts as a concurrent manager whose function is to co-ordinate the actions of database manipulation processes operating concurrently while maintaining the consistency of the shared data at the same time.

3. Recovery: The recovery mechanisms built into DBMS ensure that the database is returned to a consistent state after a transaction has failed or has been aborted.

4. Security: Security refers to protection of database from access by unauthorized users. The security levels can be varying for different users providing different access privileges so that the operations performed are monitored and controlled by the DBMS accordingly.

5. Language Interface: The DBMS provides an interface whereby the users of database create a working environment without worrying about the physical implementation. This is made possible by the data definition language and data manipulation components of the DBMS.

6. Data Catalog: Data Dictionary or Schema contains descripttions about data, relationships and constraints which can be enquired into to get information about the structure of the database.

7. Storage Manager: DBMS provide a mechanism for the management of permanent storage of data. The internal schema defines how the data should be stored by the storage manager which interfaces with the operating system to access the physical storage.