Relational model, primary key, foreign key क्या है?

The relational model, proposed by Codd in 1970, stores data as relations — tables of rows with named, typed columns — manipulated by operations on whole relations (selection, projection, join), independently of how rows are stored. A primary key is a set of columns whose values identify one row; a foreign key is a set of columns whose values must appear as the primary key of a row in another table.