Database and Database Management System (DBMS)

 

Database and Database Management System 


What is Database ?


A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organization.

Database Approach

(1) the definition of the data is embedded in the application programs, rather than being stored separately and independently

(2) there is no control over the access and manipulation of data beyond that imposed by the application programs. 


The database is a single, possibly large repository of data that can be used simultaneously by many departments and users. Instead of disconnected files with redundant data, all data items are integrated with a minimum amount of duplication. 

The database is no longer owned by one department but is a shared corporate resource. The database holds not only the organization’s operational data but also a description of this data. 

For this reason, a database is also defined as a self-describing collection of integrated records. The description of the data is known as the system catalog (or data dictionary or metadata – the ‘data about data’). It is the self-describing nature of a database that provides program–data independence .



Database Management System (DBMS)


A software system that enables users to define, create, maintain, and control access to the database.


It allows users to define the database, usually through a Data Definition Language (DDL). The DDL allows users to specify the data types and structures and the constraints on the data to be stored in the database.

It allows users to insert, update, delete, and retrieve data from the database, usually through a Data Manipulation Language (DML). Having a central repository for all data and data descriptions allows the DML to provide a general inquiry facility to this data, called a query language. 

The provision of a query language alleviates the problems with file-based systems where the user has to work with a fixed set of queries or there is a proliferation of programs, giving major software management problems. 

The most common query language is the Structured Query Language (SQL, pronounced ‘S-Q-L’, or sometimes ‘See-Quel’), which is now both the formal and de facto standard language for relational DBMSs .


It provides controlled access to the database.

For example, it may provide: 

– a security system, which prevents unauthorized users accessing the database; .

– an integrity system, which maintains the consistency of stored data

– a concurrency control system, which allows shared access of the database;

– a recovery control system, which restores the database to a previous consistent state following a hardware or software failure

– a user-accessible catalog, which contains descriptions of the data in the database .


(Database) Application Programs

A computer program that interacts with the database by issuing an program appropriate request (typically an SQL statement) to the DBMS.

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