\begin{frame}
  \frametitle{Recursive Relations}
  
  \begin{exampleblock}{}
  Example: an employee is supervised by a manager.

  \begin{center}
  \scalebox{.8}{
  \begin{tikzpicture}[every edge/.style={link},d/.style={node distance=1cm}]
    \node[entity] (employee) {employee};
      \node[attribute,at=(employee),d,shift={(170:2.5cm)}] (id) {\key{id}} edge (employee);
      \node[attribute,at=(employee),d,shift={(140:1.7cm)}] (name) {name} edge (employee);
      \node[attribute,at=(employee),d,shift={(50:1.5cm)}] (job) {job title} edge (employee);
      \node[attribute,at=(employee),d,shift={(10:2.5cm)}] (salary) {salary} edge (employee);

    \node[entity,at=(employee),shift={(7cm,0cm)}] (manager) {manager};
      \node[attribute,at=(manager),d,shift={(170:2.5cm)}] (id) {\key{id}} edge (manager);
      \node[attribute,at=(manager),d,shift={(140:1.7cm)}] (name) {name} edge (manager);
      \node[attribute,at=(manager),d,shift={(50:1.5cm)}] (job) {job title} edge (manager);
      \node[attribute,at=(manager),d,shift={(10:2.5cm)}] (salary) {salary} edge (manager);

    \node[relationship] (supervises) at ($(employee)!.5!(manager) + (0cm,-1cm)$) {supervises} edge node [below,pos=.7] {$1\sldots *$} (employee) edge node [below,pos=.7] {$0\sldots 1$} (manager);
  \end{tikzpicture}
  }
  \end{center}
  \end{exampleblock}
  \pause\medskip
  
  This diagram is \alert{wrong} since a manager is an employee as well.
\end{frame}