Transitive Dependency

Topics: Database

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In databases, we say that a relation (table) has a transitive dependency if, for three distinct sets of attributes $A$, $B$ and $C$ we have that:

1. $A\to B$ ($B$ is functionally dependant on $A$)
2. $B\nrightarrow A$ ($A$ is not functionally dependant on $B$)
3. $B\to C$

The resulting functional dependency $A\to C$ is what we call a transitive dependency. Normally we’ll refer to transitive dependencies where $A$ is a candidate key (or primary key).

Transitive dependencies are to be avoided if we want to have a relation in the third normal form.