Database Management System(DBMS) is a set of programs that enables you to store, modify, and extract information from a database, it also provides users with tools to add, delete, access, modify, and analyze data stored in one location. A group can access the data by using query and reporting tools that are part of the DBMS or by using application programs specifically written to access the data. DBMS’s also provide the method for maintaining the integrity of stored data, running security and users access, and recovering information if the system fails. The information from a database can be presented in a variety of formats. Most DBMSs include a report writer program that enables you to output data in the form of a report. Many DBMSs also include a graphics component that enables you to output information in the form of graphs and charts. Database and database management system are essential to all areas of business, they must be carefully managed. There are many different types of DBMSs, ranging from small systems that run on personal computers to huge systems that run on mainframes.

The following are examples of database applications: computerized library systems, flight reservation systems, and computerized parts inventory systems. It typically support squery languages, which are in fact high-level programming languages, dedicated database languages that considerably simplify writing database application programs. Database languages also simplify the database organization as well as retrieving and presenting information from it. A DBMS provides facilities for controlling data access, enforcing data integrity, managing concurrency control, and recovering the database after failures and restoring it from backup files, as well as maintaining database security.

The major components of a DBMS are shown in the following figure.

Services provided by a DBMS

Services provided by a DBMS

We will see the services provided by a DBMS in some detail in the following sections:

Transaction Management

A transaction is a sequence of database operations that represents a logical unit of work and that accesses a database and transforms it from one state to another. A transaction can update a record, delete one, modify a set of records, etc. When the DBMS does a 'commit' the changes made by the transaction are made permanent. If you don't want to make the changes permanent you can rollback the transaction and the database will remain in its original state.

Concurrency Control

Concurrency control is the database management activity of coordinating the actions of database manipulation processes that operate concurrently that access shared data and can potentially interfere with one another. The goal of an ideal concurrency management mechanism is to allow concurrency while maintaining the consistency of the shared data.

Recovery Management

The recovery management system in a database ensures that the aborted or failed transactions create no adverse effects on the database or the other transactions. Recovery mechanisms in a DBMS make sure that the database is returned to a consistent state after a transaction fails or aborts. Recovery is very much related to concurrency in the sense that, the mote the concurrency the more is the chance that an aborted transaction can affect many other transactions.

Security Management

Security refers to the protection of data against unauthorized access. Security mechanisms of a DBMS make sure that only authorized users are given access to the data in the database. The level of access for each user and the operations that each user can perform on the data will be monitored and controlled by the DBMS depending on the access privileges of the users.

Language Interface

The DBMS provides support languages used for the definition and manipulation of the data in the database. The data structures are created using the data definition language commands. The data manipulation is done using the data manipulation commands. By providing the language support for data definition and manipulation the DBMS creates an environment where the users can do their jobs without worrying about the physical implementation.

Storage Management

The DBMS provides a mechanism for management of permanent storage of the data. The internal schema defines how the data should be stored by the storage management mechanism and the storage manager interfaces with the operating system to access the physical storage.

Data Catalog Management

Data Catalog or Data Dictionary is a system database that contains descriptions of the data in the database (metadata). It contains information about data, relationships, constraints and the entire schema that organize these features into a unified database. The data catalog can be queried to get information about the structure of the database.

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