\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}