Codd's rule of entity integrity stipulates the existence of a primary key over every database
table. That is, uniqueness and absence of null markers are enforced on the columns of the
primary key. Key sets stipulate a generalized entity integrity rule that can be achieved on
data sets where primary keys do not exist. Indeed, a key set means that different pairs of
rows can be distinguished by unique non-null values on potentially different elements of the
key set. While primary keys are a core feature of SQL databases, key sets have not been …

Codd's rule of entity integrity stipulates the existence of a primary key over every database
table. That is, uniqueness and absence of null markers are enforced on the columns of the
primary key. Key sets stipulate a generalized entity integrity rule that can be achieved on
data sets where primary keys do not exist. Indeed, a key set means that different pairs of
rows can be distinguished by unique non-null values on potentially different elements of the
key set. While primary keys are a core feature of SQL databases, key sets have not been …