What are Codd’s Rules?

Codd’s Rules that are 12 in number specify what a database must support in order to be relational. The rules were defined by Edgar F Codd in a paper published in 1985. Hence, they are known as Codd’s Rules. For example, data are represented only one way; as values within columns and rows. Every value can be assessed by providing table name, column name and key, and all data are unique.