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Definition: Referential integrity is a database concept that ensures that relationships between tables remain consistent. When one table has a foreign key to another table, the concept of referential integrity states that you may not add a record to the table that contains the foreign key unless there is a corresponding record in the linked table.
Data integrity is normally enforced in a database system by a series of integrity constraints or rules. Three types of integrity constraints are an inherent part of the relational data model: entity integrity, referential integrity and domain integrity. Entity integrity concerns the concept of a primary key. Entity integrity is an integrity ...
This rule is called a referential integrity constraint between the two tables. [5] Because violations of these constraints can be the source of many database problems, most database management systems provide mechanisms to ensure that every non-null foreign key corresponds to a row of the referenced table. [6] [7] [8]
Constraints can apply to single attributes, to a tuple (restricting combinations of attributes) or to an entire relation. Since every attribute has an associated domain, there are constraints (domain constraints). The two principal rules for the relational model are known as entity integrity and referential integrity.
If a referential integrity constraint is defined to the effect that {Shop type, Nearest shop} from the first table must refer to a {Shop type, Shop} from the second table, then the data anomalies described previously are prevented.
Facilities for defining uniqueness constraints and referential integrity are more powerful: unlike the ID and IDREF constraints in DTDs, they can be scoped to any part of a document, can be of any data type, can apply to element as well as attribute content, and can be multi-part (for example the combination of first name and last name must be ...
Entity integrity is concerned with ensuring that each row of a table has a unique and non-null primary key value; this is the same as saying that each row in a table represents a single instance of the entity type modelled by the table. A requirement of E. F. Codd in his seminal paper is that a primary key of an entity, or any part of it, can ...
The term integrity encompasses accuracy, consistency and some aspects of validation (see also data integrity) but is rarely used by itself in data-cleansing contexts because it is insufficiently specific. (For example, "referential integrity" is a term used to refer to the enforcement of foreign-key constraints above.)