Integrity

Data integrity

Data Integrity in its broadest meaning refers to the trustworthiness of system resources over their entire life cycle. In more analytic terms, it is "the representational faithfulness of information to the true state of the object that the information represents, where representational faithfulness...

 constraints are used to ensure accuracy and consistency of data in a relational database

Relational database

A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...

. Data integrity is handled in a relational database through the concept of referential integrity

Referential integrity

Referential integrity is a property of data which, when satisfied, requires every value of one attribute of a relation to exist as a value of another attribute in a different relation ....

. There are many types of integrity constraints that play a role in referential integrity.

Types

Codd

Edgar F. Codd

Edgar Frank "Ted" Codd was an English computer scientist who, while working for IBM, invented the relational model for database management, the theoretical basis for relational databases...

initially defined two sets of constraints but, in his second version of the relational model, he came up with five integrity constraints:

Entity integrity

The entity integrity constraint states that no primary key value can be null. This is because the primary key value is used to identify individual tuples in a relation . Having null value for the primary key implies that we cannot identify some tuples.This also specifies that there may not be any duplicate entries in primary key column key row.

Referential Integrity

The referential integrity constraint is specified between two relations and is used to maintain the consistency among tuple's in the two relations. Informally, the referential integrity constraint states that a tuple in one relation that refers to another relation must refer to an existing tuple in that relation.It is a rule that maintains consistency among the rows of the two relations

Domain Integrity

The domain integrity states that every element from a relation should respect the type and restrictions of its corresponding attribute. A type can have a variable length which needs to be respected. Restrictions could be the range of values that the element can have, the default value if none is provided, and if the element can be NULL.