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A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as invented by E. F. Codd, of IBM's San Jose Research Laboratory. Many popular databases currently in use are based on the relational database model. RDBMSs are a common choice for the storage of information in new databases used for financial records, manufacturing and logistical information, personnel data, and other applications since the 1980s. Relational databases have often replaced legacy hierarchical databases and network databases because they are easier to understand and use. However, relational databases have received unsuccessful challenge attempts by object database management systems in the 1980s and 1990s (which were introduced trying to address the so-called object-relational impedance mismatch between relational databases and object-oriented application programs) and also by XML database management systems in the 1990s. Despite such attempts, RDBMSs keep most of the market share, which has also grown over the years. ==Market share== According to research company Gartner, the five leading commercial relational database vendors by revenue in 2011 were Oracle (48.8%), IBM (20.2%), Microsoft (17.0%), SAP including Sybase (4.6%), and Teradata (3.7%).〔(【引用サイトリンク】date=2012-04-12 )〕 The three leading open source implementations are MySQL, PostgreSQL, and SQLite. MariaDB is a prominent fork of MySQL prompted by Oracle's acquisition of MySQL AB. According to Gartner, in 2008, the percentage of database sites using any given technology were (a given site may deploy multiple technologies):〔(【引用サイトリンク】accessdate=2013-03-01 )〕 *Oracle Database - 70% *Microsoft SQL Server - 68% *MySQL (Oracle Corporation) - 50% *IBM DB2 - 39% *IBM Informix - 18% *SAP Sybase Adaptive Server Enterprise - 15% *SAP Sybase IQ - 14% *Teradata - 11% According to DB-Engines, the most popular systems are Oracle, MySQL, Microsoft SQL Server, PostgreSQL and IBM DB2.〔(【引用サイトリンク】accessdate=2013-05-06 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Relational database management system」の詳細全文を読む スポンサード リンク
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