\begin{frame} \frametitle{Preservation of Functional Dependencies} \vspace{-.75ex} \begin{goal}{} Besides losslessness, a desirable property of a decomposition is the \emph{preservation of functional dependencies}: \begin{itemize} \item A FD can refer only to attributes of a single relation. \item When splitting a relation into two, there might be FDs that can no longer be expressed (they are not preserved). \end{itemize} \end{goal} \pause \begin{exampleblock}{FD gets lost during decomposition} \exampleZip \pause The second FD violates BCNF and would lead to the split: \begin{itemize} \item \sql{Addresses1(streetAddress, city, zip)} \item \sql{Addresses2(zip, state)} \end{itemize} \pause \alert{But now the first FD can no longer be expressed.} \hfill\smash\textdbend \end{exampleblock} \end{frame}