What is a database management system?

While a database is a repository of data, a database management system, or simply DBMS, is a set of software tools that control access, organize, store, manage, retrieve and maintain data in a database. In practical use, the terms database, database server, database system, data server, and database management systems are often used interchangeably.
The most mature database systems in production are relational database management systems (RDBMS’s). RDBMS's serve as the backbone of applications in many industries including banking, transportation, health, and so on. The advent of Web-based interfaces has only increased the volume and breadth of use of RDBMS, which serve as the data repositories behind essentially most online commerce.
In the 1960s, network and hierarchical systems such as CODASYL and IMSTM were the state-of-the-art technology for automated banking, accounting, and order processing systems enabled by the introduction of commercial mainframe computers. While these systems provided a good basis for the early systems, their basic architecture mixed the physical manipulation of data with its logical manipulation. When the physical location of data changed, such as from one area of a disk to another, applications had to be updated to reference the new location.
A revolutionary paper by E.F. Codd, an IBM San Jose Research Laboratory employee in 1970, changed all that. The paper titled “A relational model of data for large shared data banks” introduced the notion of data independence, which separated the physical representation of data from the logical representation presented to applications. Data could be moved from one part of the disk to another or stored in a different format without causing applications to be rewritten. Application developers were freed from the tedious physical details of data manipulation, and could focus instead on the logical manipulation of data in the context of their specific application.
Today, relational database management systems are the most used DBMS's and are developed by several software companies. IBM is one of the leaders in the market with DB2 database server. Other relational DBMS's include Oracle, Microsoft SQL Server, INGRES, PostgreSQL, MySQL, and dBASE.
As increased amounts of data were collected and stored in databases, DBMS's scaled. In DB2 for Linux, UNIX and Windows, for example, a feature called Database Partitioning Feature (DPF) allows a database to be spread across many machines using a shared-nothing architecture. Each machine added brings its own CPUs and disks; therefore, it is easier to scale almost linearly. A query in this environment is parallelized so that each machine retrieves portions of the overall result.
Next in the evolution of DBMS's is the concept of extensibility. The Structured Query Language (SQL) invented by IBM in the early 1970's has been constantly improved through the years. Even though it is a very powerful language, users are also empowered to develop their own code that can extend SQL. For example, in DB2 you can create user-defined functions, and stored procedures, which allow you to extend the SQL language with your own logic.

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