\begin{frame}
  \frametitle{ER Models vs. UML Class Diagrams}

  \begin{goal}{Generalisation and Specialisation}
  \begin{minipage}{.49\textwidth}
    \begin{center}
    \scalebox{.9}{
    \begin{tikzpicture}[every edge/.style={link},d/.style={node distance=1cm}]
      \node[entity] (person) {person};
      \node[entity,at=(person),shift={(-1.5cm,-2.4cm)}] (employee) {employee};
      \node[entity,at=(person),shift={(1.5cm,-2.4cm)}] (customer) {customer};
      \node[isa,at=(person),shift={(0cm,-0.7cm)}] {ISA} edge (person) edge (employee) edge (customer);
    \end{tikzpicture}
    }
    \end{center}
  \end{minipage}
  \begin{minipage}{.49\textwidth}
    \begin{center}
    \quad\quad\begin{tikzpicture}[nodes={xscale=.8}]
    \umlsimpleclass[width=5mm]{employee}
    \umlsimpleclass[x=3cm,width=5mm]{customer}
    \umlsimpleclass[x=1.5cm,y=2cm,width=5mm]{person}
    \umlinherit{customer}{person} 
    \umlinherit{employee}{person} 
    \draw[dashed] (0cm,1cm) -- node [pos=1,above,inner sep=.5mm] {{\scriptsize overlapping}} (3.2cm,1cm);
    \end{tikzpicture} 
    \end{center}
  \end{minipage}
  \bigskip\bigskip
  
  \begin{minipage}{.49\textwidth}
    \begin{center}
    \scalebox{.9}{
    \begin{tikzpicture}[every edge/.style={link},d/.style={node distance=1cm}]
      \node[entity] (person) {person};
      \node[entity,at=(person),shift={(-1.5cm,-2.4cm)}] (employee) {employee};
      \node[entity,at=(person),shift={(1.5cm,-2.4cm)}] (customer) {customer};
      \node[isa,at=(person),shift={(0cm,-0.7cm)}] (ISA) {ISA} edge (person) edge (employee) edge (customer);
      \node [ro=ISA,yshift=-5mm] {{\scriptsize disjoint}};
    \end{tikzpicture}
    }
    \end{center}
  \end{minipage}
  \begin{minipage}{.49\textwidth}
    \begin{center}
    \quad\quad\begin{tikzpicture}[nodes={xscale=.8}]
    \umlsimpleclass[width=5mm]{employee}
    \umlsimpleclass[x=3cm,width=5mm]{customer}
    \umlsimpleclass[x=1.5cm,y=2cm,width=5mm]{person}
    \umlVHVinherit{customer}{person} 
    \umlVHVinherit{employee}{person} 
    \node [above,inner sep=.5mm] at (3.2cm,1cm) {{\scriptsize disjoint}};
    \end{tikzpicture} 
    \end{center}
  \end{minipage}
  \end{goal}
\end{frame}