Dependency theory is a subfield of

database theory Database theory encapsulates a broad range of topics related to the study and research of the theoretical realm of databases and database management systems. Theoretical aspects of data management include, among other areas, the foundations of qu ...

which studies implication and optimization problems related to logical constraints, commonly called dependencies, on databases. The best known class of such dependencies are functional dependencies, which form the foundation of

keys Key or The Key may refer to: Common meanings * Key (cryptography), a piece of information that controls the operation of a cryptography algorithm * Key (lock), device used to control access to places or facilities restricted by a lock * Key (ma ...

on database relations. Another important class of dependencies are the

multivalued dependencies In database theory, a multivalued dependency is a full constraint between two sets of attributes in a relation. In contrast to the functional dependency, the multivalued dependency requires that certain tuples be present in a relation. Therefore, ...

. A key algorithm in dependency theory is the

chase Chase or CHASE may refer to: Businesses * Chase Bank, a national bank based in New York City, New York * Chase Aircraft (1943–1954), a defunct American aircraft manufacturing company * Chase Coaches, a defunct bus operator in England * Chase Co ...

, and much of the theory is devoted to its study.

Dependencies

functional dependency In relational database theory, a functional dependency is a constraint between two sets of attributes in a relation from a database. In other words, a functional dependency is a constraint between two attributes in a relation. Given a relation '' ...

join dependency In database theory, a join dependency is a constraint on the set of legal relations over a database scheme. A table T is subject to a join dependency if T can always be recreated by joining multiple tables each having a subset of the attributes of ...

multivalued dependency In database theory, a multivalued dependency is a full constraint between two sets of attributes in a relation. In contrast to the functional dependency, the multivalued dependency requires that certain tuples be present in a relation. Therefore, ...

tuple-generating dependency In relational database theory, a tuple-generating dependency (TGD) is a certain kind of constraint on a relational database. It is a subclass of the class of embedded dependencies (EDs). An algorithm known as the chase takes as input an instance ...

equality-generating dependency In relational database theory, an equality-generating dependency (EGD) is a certain kind of constraint on data. It is a subclass of the class of embedded dependencies (ED). An algorithm known as the chase takes as input an instance that may or m ...

embedded dependency In relational database theory, an embedded dependency (ED) is a certain kind of constraint on a relational database. It is the most general type of constraint used in practice, including both tuple-generating dependencies and equality-generating de ...

inclusion dependency Referential integrity is a property of data stating that all its references are valid. In the context of relational databases, it requires that if a value of one attribute (column) of a relation (table) references a value of another attribute (e ...

full typed dependency Full may refer to: * People with the surname Full, including: ** Mr. Full (given name unknown), acting Governor of German Cameroon, 1913 to 1914 * A property in the mathematical field of topology; see Full set * A property of functors in the mathe ...

{{database-stub Database theory Database constraints