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 may not satisfy a set of EGDs (or, more generally, a set of EDs), and, if it terminates (which is a priori undecidable), output an instance that does satisfy the EGDs.
An important subclass of equality-generating dependencies are functional dependencies.
An equality-generating dependency is a sentence in first-order logic of the form: where
is a conjunction of relational and equality atoms and
is a non-empty conjunction of equality atoms.
A relational atom has the form
and an equality atom has the form
are variables or constants.
Actually, one can remove all equality atoms from the body of the dependency without loss of generality.
[1] For instance, if the body consists in the conjunction
(analogously replacing possible occurrences of the variables
An equivalent definition is the following:[2] where
Indeed, generating a conjunction of equalities is equivalent to have multiple dependencies which generate only one equality.
This database-related article is a stub.