Relational Database Systems

In 1970, E. F. Codd of the IBM Research Laboratory published a paper on the relational data model. In this paper he described a new system (i.e. relational database model) for storing and working  with large databases. He applied the concepts of relational algebra ( a branch of mathematics) to describe the new system. Instead of records being stored in some sort of linked list of free-form records as in CODASYL, his concept was to use a "table" of fixed-length records. Many experimental relational database management systems were implemented thereafter, with the first commercial products appearing in the late 1970s and early 1980s. IBM started working on a prototype system based on Codd's concepts e.g., System R in the early 1970s. This project led to two major developments:

1. The development of a structured query language called SQL, which has since become the standard language for relational systems.
2. The production of various commercial relational DBMS products during the 1980s, for example DB2 from IBM and ORACLE from ORACLE Corporation.

Now there are several hundred relational database management systems for both mainframe and microcomputer environments, though many are following the concept of the relational model. Other examples of multi-user  relational database managements system are INGRES from Computer Associates, and INFORMIX from Informix Software Inc. and SYBASE from Sybase Inc.
In 1979, dBase-II was developed by Ashton-Tare and it was called as relational DBMS. It was very popular in PCs. It was not a truly relational DBMS product. In face, it was a programming language with generalized file-processing capabilities.