\begin{frame}
  \frametitle{Keys are Functional Dependencies}
  
  \begin{block}{Keys are functional dependencies}
    $\{\, A_1, \dots, A_n \,\}$ is a key of relation $R(A_1,\dots,A_n,B_1,\dots,B_m)$\\
    $\iff$ the functional dependency $A_1, \dots, A_n \to B_1, \dots B_m$ holds.
  \end{block}
  A \emph{key} uniquely determines \emph{all} attributes of its relation.
  \pause\medskip
  
  \begin{exampleblock}{}
    \begin{center}
      \tableCourses
    \end{center}
    We have the following functional dependencies:
    \begin{tcenter}
      $\sql{courseNr} \to \sql{title}, \sql{instructor}, \sql{phone}$
    \end{tcenter}
    or equivalently:
    \begin{tcenter}
      $\sql{courseNr} \to \sql{title}$ \\
      $\sql{courseNr} \to \sql{instructor}$ \\
      $\sql{courseNr} \to \sql{phone}$ 
    \end{tcenter}
  \end{exampleblock}
\end{frame}