A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced 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 have become a predominant choice for the storage of information in new databases used for financial records, manufacturing and logistical information, personnel data, and much more 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 been challenged by object databases, which were introduced in an attempt to address the object-relational impedance mismatch in relational database, and XML databases
According to research company Gartner, the five leading commercial relational database vendors by revenue in 2001 were Oracle (48.8%), IBM (20.2%), Microsoft(17.0%), SAP including Sybase (4.6%), and Teradata (3.7%).
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):[2]
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.[3]