A functional http://wiki.answers.com/wiki/Dependency_theory_(database_theory) (FD) is a constraint between two sets of attributes in a http://wiki.answers.com/wiki/Relational_model from a...
Functional Dependency.
Functional Dependencies A Functional Dependency describes a relationship between attributes in a single relation. An attribute is functionally dependant on another if we can...
-->non trivial functional dependency is totally opposite to the trivial functional dependency.--> non trivial dependency means X-->Y that is if Y is not proper subset of X table or relation...
A key is a set of attributes that uniquely identifies an entire tuple, a function dependency allow us to express constraints that uniquely identify the values of certain attribute.