Equality-generating dependency
In relational database theory, an equality-generating dependency is a certain kind of constraint on data. It is a subclass of the class of embedded dependencies. An ED is a sentence in first-order logic of the form:
∀x1... xn, P → ∃z1,..., zk, Q
where = \, and P is a possibly empty and Q is a non-empty conjunction of equality atoms. A n equality atom has the form wi = wj where each of the w,..., wh, wi, wj, are variables or constants. An algorithm known as the chase takes as input an instance that may or may not satisfy a set of EGDs, and, if it terminates, output an instance that does satisfy the EGDs.
An important subclass of equality-generating dependencies are functional dependencies.
