Structured Query Language (SQL) is a standardized, widely
used language that retrieves and updates data in relational tables
and databases.
A
relation is a mathematical concept that is similar to
the mathematical concept of a set. Relations are represented physically
as two-dimensional tables that are arranged in rows and columns. Relational
theory was developed by E. F. Codd, an IBM researcher, and first implemented
at IBM in a prototype called System R. This prototype evolved into
commercial IBM products based on SQL. The Structured Query Language
is now in the public domain and is part of many vendors' products.