Relational database RDBMS
DB model based on tables (relations) with rows + columns. Query language: SQL. Edgar F. Codd, IBM, 1970. Dominated the DB market for 40+ years.
Major implementations: PostgreSQL, MySQL, Oracle, SQL Server, SQLite. ACID properties (atomicity, consistency, isolation, durability). Built on relational algebra. Join is the central operation. The NoSQL wave 2009–2015 was a counter-movement → mostly faded (PostgreSQL today does JSON, graph, vector, time-series). NewSQL (CockroachDB, Spanner) tried to fill the scalability gap without losing SQL.