In his seminal 1970 paper “A Relational Model of Data for Large Shared Data Banks,” E. F. Codd defined a relational model based on mathematical set theory. Today, the most widely accepted database model is the relational model.
A relational database is a database that conforms to the relational model. The relational model has the following major aspects:
Well-defined objects store or access the data of a database.
Clearly defined actions enable applications to manipulate the data and structures of a database.
Integrity rules govern operations on the data and structures of a database.
A relational database stores data in a set of simple relations. A relation is a set of tuples (rows). A tuple is an unordered set of attribute (columns) values.
A table is a two-dimensional representation of a relation in the form of rows (tuples) and columns (attributes). Each row in a table has the same set of columns. A relational database is a database that stores data in relations (tables). For example, a relational database could store information about company employees in an employee table, a department table, and a salary table.