\begin{frame} \frametitle{Fourth Normal Form} \begin{block}{Fourth Normal Form (4NF)} A relation is in \emph{Fourth Normal Form (4NF)} if every MVD \begin{center} $A_1, \dots, A_n \mvd B_1,\dots, B_m$ \end{center} is \begin{itemize} \item either trivial, or \item implied by a key. \end{itemize} \end{block} This definition of 4NF is very similar to BCNF but with a focus on implied MVDs (not FDs). \pause\medskip \begin{goal}{} Since every FD is also an MVD, 4NF is stronger than BCNF.\\ \remark{% That is, if a relation is in 4NF, it is automatically in BCNF. } \end{goal} \remark{% However, it is not very common that 4NF is violated, but BCNF is not. } \end{frame}