Functional Dependency

Third Normal Form (3NF)

Learned in CS348.

Haven’t practiced this yet, but this video shows. Transformation to 3NF video.

Third Normal Form (3NF)

Schema $R$ is in 3NF with respect to a set of functional dependencies $F$ if and only if, whenever $(X\to Y)\in F^{+}$ and $XY\subseteq R$, then either

• $(X\to Y)$ is trivial,
• $X$ is a superkey of $R$, or
• each attribute of $Y-X$ is contained in a candidate key of $R$.

A database schema $⟨\rho =\{R_1,...,R_n\},F⟩$ is in 3NF if each relation schema $R_i$ is in 3NF with respect to $F$.

• So basically, it is a more flexible version of BCNF, where you can have the LHS not be a candidate key, as long as it functionally determines a candidate key

Computing a 3NF Decomposition

• Watch this? Not sure if it is the same thing https://www.youtube.com/watch?v=DwwQFTRcG7M&list=PL3TE2CsKK478JNAXYLD_hzQFx5JE360KO&index=52&ab_channel=TheoreticalComputerScience