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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 ...
Codd's twelve rules [1] are a set of thirteen rules (numbered zero to twelve) proposed by Edgar F. Codd, a pioneer of the relational model for databases, designed to define what is required from a database management system in order for it to be considered relational, i.e., a relational database management system (RDBMS).
The formal definition of a database schema is a set of formulas (sentences) called integrity constraints imposed on a database. [citation needed] These integrity constraints ensure compatibility between parts of the schema. All constraints are expressible in the same language. A database can be considered a structure in realization of the ...
An example of a database that has not enforced referential integrity. In this example, there is a foreign key ( artist_id ) value in the album table that references a non-existent artist — in other words there is a foreign key value with no corresponding primary key value in the referenced table.
The SQL/Schemata, or Information and Definition Schemas, part of the SQL standard is defined by ISO/IEC 9075-11:2008.SQL/Schemata defines the information schema and definition schema, providing a common set of tools to make SQL databases and objects self-describing.
The enforcement of a key constraint (i.e. a uniqueness constraint) in a table is also a data integrity feature of the database. The DBMS prevents updates that would cause duplicate key values and thereby ensures that tables always comply with the desired rules for uniqueness.
The DBMS must reject a transaction such as this that would render the database inconsistent by a violation of an integrity constraint. However, it is possible to insert another customer named Alice , as long as this new customer has a unique ID, since the Name field is not part of the primary key.
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd [12] in the early 1970s. [13] This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...