Database

Database is a set of data organized in accordance with certain rules and maintained in the computer memory, characterizing the current state of a certain subject area, and used to meet the information needs of users.

There are many definitions of the concept of "database,” reflecting rather the subjective opinion of certain authors, but there is no generally accepted uniform definition. Other examples of database definitions are as follows:

• A database is a set of permanently stored data used by the application software, or by the individual to structurize massive amount of information.
• A database is a shared set of logically related data designed to meet the user's information needs.

Database management system (DBMS) - is a set of programs that enables you to keep, extract, and modify information from a database.

There are different types of DBMS, from small systems running on PCs to large systems, which run on mainframes.

Main functions of DBMS

• Data management in external memory (on disks);
• Data management in RAM using disk cache;
• Logging changes, backing up and restoring the database after a failure;
• Database languages support (data definition and manipulation languages).

A very large database (VLDB) is a database that occupies an extremely large volume on a physical storage device. The term implies the maximum possible volumes of databases, which are determined by the latest achievements in the technologies of physical data storage and software operations.

Classification by degree of distribution

• Centralized: A database fully supported on one computer.
• Distributed: Component parts are located in different nodes of the computer network in accordance with some criterion.
• Heterogeneous distribution: fragments of a distributed database in different nodes of the network are supported by more than one DBMS.
• Homogeneous distribution: fragments of a distributed database in different nodes of the network are supported by the same DBMS.
• Fragmented: the method of data distribution is fragmentation, vertical or horizontal.
• Replicated: the method of distribution is replication.
  
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