the underlying database is relational. An alternative definition for a relational database management system is a database management system (DBMS) based on the relational model. Most databases in widespread use today are based on this model. RDBMSs have been a common option for the storage of information in 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 RDBMS were easier to implement and administer. Nonetheless, relational stored data received continued, unsuccessful challenges by object database management systems in the 1980s and 1990s, (which were introduced in an attempt to address the so-called object–relational impedance mismatch between relational databases and object-oriented application programs), as well as by XML database management systems in the 1990s. However, due to the expanse of technologies, such as horizontal scaling of computer clusters, NoSQL databases have recently become popular as an alternative to RDBMS databases. Distributed relational databases Distributed Relational Database Architecture (DRDA) was designed by a workgroup within IBM in the period 1988 to 1994. DRDA enables network connected relational databases to cooperate to fulfill SQL requests. The messages, protocols, and structural components of DRDA are defined by the Distributed Data Management Architecture. Market share According to DB-Engines, in January 2023 the most popular systems on the db-engines.com web site were: Oracle Database MySQL Microsoft SQL Server PostgreSQL (free software) IBM Db2 Microsoft Access SQLite (free software) MariaDB (free software) Snowflake Microsoft Azure SQL Database Apache Hive (free software) Teradata Vantage According to research company Gartner, in 2011, the five leading proprietary software relational database vendors by revenue were Oracle (48.8%), IBM (20.2%), Microsoft (17.0%), SAP including Sybase (4.6%), and Teradata (3.7%). See also SQL Object database (OODBMS) Online analytical processing (OLAP) and ROLAP (Relational Online Analytical Processing) Data warehouse Star schema Snowflake schema List of relational database management systems Comparison of relational database management systems References Sources External links Relational model Database theory Types of databases English inventions Computer-related introductions in 1969