A database is a system intended to organize, store, and retrieve large amounts of data easily. It consists of an organized collection of data for one or more uses, typically in digital form. One way of classifying databases involves the type of their contents, for example: bibliographic, document-text, statistical. Digital databases are managed using database management systems, which store database contents, allowing data creation and maintenance, and search and other access.

Architecture

Database architecture consists of three levels, external, conceptual and internal. Clearly separating the three levels was a major feature of the relational database model that dominates 21st century databases.

The external level defines how users understand the organization of the data. A single database can have any number of views at the external level. The internal level defines how the data is physically stored and processed by the computing system. Internal architecture is concerned with cost, performance, scalability and other operational matters.

Database management systems

A database management system (DBMS) consists of software that operates databases, providing storage, access, security, backup and other facilities. Database management systems can be categorized according to the database model that they support, such as relational or XML, the type(s) of computer they support, such as a server cluster or a mobile phone, the query language(s) that access the database, such as SQL or XQuery, performance trade-offs, such as maximum scale or maximum speed or others.

Examples of some commonly used DBMS are MySQL, PostgreSQL, Microsoft Access, SQL Server, FileMaker,Oracle,Sybase, dBASE, Clipper,FoxPro etc. Almost every database software comes with an Open Database Connectivity (ODBC) driver that allows the database to integrate with other databases.

Type

• Operational database: These databases store detailed data about the operations of an organization. Examples include customer databases that record contact, credit, and demographic information about a business’ customers, personnel databases that hold information such as salary, benefits, skills data about employees, Enterprise resource planning that record details about product components, parts inventory, and financial databases that keep track of the organization’s money, accounting and financial dealings.
• Data warehouse: Data warehouses archive modern data from operational databases and often from external sources such as market research firms. The warehouse becomes the central source of data for use by managers and other end-users who may not have access to operational data. Some basic and essential components of data warehousing include retrieving and analyzing data, transforming, loading and managing data so as to make it available for further use.
• Analytical database: Analysts may do their work directly against, a data warehouse, or create a separate analytic database for Online Analytical Processing. For example, a company might extract sales records for analyzing the effectiveness of advertising and other sales promotions at an aggregate level.
• Distributed database: These are databases of local work-groups and departments at regional offices, branch offices, manufacturing plants and other work sites. These databases can include segments of both common operational and common user databases, as well as data generated and used only at a user’s own site.
• End-user database: These databases consist of data developed by individual end-users. Examples of these are collections of documents in spreadsheets, word processing and downloaded files, even managing their personal baseball card collection.
• External database: These databases contain data collected for use across multiple organizations, either freely or via subscription. The Internet Movie Database is one example.
• Hypermedia databases: The Worldwide web can be thought of as a database, albeit one spread across millions of independent computing systems. Web browsers “process” this data one page at a time, while web crawlers and other software provide the equivalent of database indexes to support search and other activities.

Additional Areas of Focus

• Data hierarchy
• Database design
• Database-centric architecture
• Data-structuring
• Document-oriented databases
• In-memory databases
• Real time databases
• Web databases