This section is missing information about early history in this section given the Micro DBMS relational database in 1969 before Codd invented the term in 1970 ... . (April 2019)
The term "relational database" was invented by E. F. Codd at IBM in 1970. Codd introduced the term in his research paper "A Relational Model of Data for Large Shared Data Banks".
In this paper and later papers, he defined what he meant by "relational". One well-known definition of what constitutes a relational database system is composed of Codd's 12 rules. However, no commercial implementations of the relational model conform to all of Codd's rules, so the term has gradually come to describe a broader class of database systems, which at a minimum:
- Present the data to the user as relations (a presentation in tabular form, i.e. as a collection of tables with each table consisting of a set of rows and columns);
- Provide relational operators to manipulate the data in tabular form.
In 1974, IBM began developing System R, a research project to develop a prototype RDBMS.
However, the first commercially available RDBMS was Oracle, released in 1979 by Relational Software, now Oracle Corporation.
Other examples of an RDBMS include DB2, SAP Sybase ASE, and Informix. In 1984, the first RDBMS for Macintosh began being developed, code-named Silver Surfer, it was later released in 1987 as 4th Dimension and known today as 4D.
The first systems that were relatively faithful implementations of the relational model were from:
- University of Michigan -- Micro DBMS (1969)
- Massachusetts Institute of Technology (1971)
- IBM UK Scientific Centre at Peterlee -- IS1 (1970–72) and its successor, PRTV (1973–79)
The first system sold as an RDBMS was Multics Relational Data Store (1978). Ingres and IBM BS12 followed.
The most commonly definition of an RDBMS is a product that presents a view of data as a collection of rows and columns, even if it is not based strictly upon relational theory. By this definition, RDBMS products typically implement some but not all of Codd's 12 rules.
A second school of thought argues that if a database does not implement all of Codd's rules (or the current understanding on the relational model, as expressed by Christopher J Date, Hugh Darwen and others), it is not relational. This view, shared by many theorists and other strict adherents to Codd's principles, would disqualify most DBMSs as not relational. For clarification, they often refer to some RDBMSs as truly-relational database management systems (TRDBMS), naming others pseudo-relational database management systems (PRDBMS).
As of 2009, most commercial relational DBMSs employ SQL as their query language.
Alternative query languages have been proposed and implemented, notably the pre-1996 implementation of Ingres QUEL.