Part III. Relational Databases and SQL

A relational database consists of a finite set of relational tables, which are finite set-theoretic relations over elementary data types, i.e. sets of corresponding uniform tuples forming the rows of the table.

The Relational Database Model was proposed by E.F. Codd in 1970[1] and proved to be the most viable model for databases. This is mainly due to the fact that it is based on the simple mathematical-logical concept of relations (or tables) and therefore particularly well supports the storage and processing of propositional information.

SQL

The Structured Query Language (SQL), created in the early 1970s by Donald D. Chamberlin and Raymond F. Boyce, is an ISO standard that is based on the Relational Database model of Edgar F. Codd and defines

a Data Definition Language, based on CREATE TABLE statements, for creating databases consisting of tables containing primitive data;
a Data Manipulation Language, based on INSERT, UPDATE and DELETE statements, for creating, updating and deleting the contents of database tables;
a Query Language, based on SELECT statements, for retrieving the information stored in database tables.

SQL is widely used in Database Management Systems (DBMSs) and in programming languages for persistent data storage. Despite the existence of the SQL standard, each SQL DBMS has its own dialect of SQL. Consequently, SQL code is in practice not completely portable among different DBMSs without adjustments.

[1] E.F. Codd. 1970. A Relational Model of Data for Large Shared Data Banks. Communications of the ACM, Volume 13, Number 6 (June 1970), 377-387.