\begin{frame}
  \frametitle{IS-A, `Inheritance'}
  
  \begin{exampleblock}{}
    \begin{center}
    \scalebox{.9}{
    \begin{tikzpicture}[every edge/.style={link},d/.style={node distance=1cm}]
      \node[entity] (person) {person};
        \node[attribute,above of=person,d,xshift=-1.2cm] (name) {name} edge (person);
        \node[attribute,above of=person,d,xshift=1.2cm] (address) {address} edge (person);

      \node[entity,at=(person),shift={(-1.5cm,-2.4cm)}] (employee) {employee};
        \node[attribute,above left of=employee,node distance=1.6cm,xshift=-.5cm] (salary) {salary} edge (employee);

      \node[entity,at=(person),shift={(1.5cm,-2.4cm)}] (customer) {customer};
        \node[attribute,above right of=customer,node distance=1.6cm,xshift=.5cm] (credit-rating) {credit-rating} edge (customer);

      \node[isa,at=(person),shift={(0cm,-0.8cm)}] {ISA} edge (person) edge (employee) edge (customer);

      \node[entity,at=(employee),shift={(-2cm,-2.7cm)}] (officer) {officer};
        \node[attribute,below left of=officer,node distance=1.6cm,xshift=-.5cm] (office-number) {office-number} edge (officer);
      \node[entity,at=(employee),shift={(0cm,-2.7cm)}] (teller) {teller};
        \node[attribute,below left of=teller,node distance=2.8cm,xshift=0cm] (station-number) {station-number} edge (teller);
        \node[attribute,below right of=teller,node distance=2.8cm,xshift=0cm] (hours-worked) {hours-worked} edge (teller);
      \node[entity,at=(employee),shift={(2cm,-2.7cm)}] (secretary) {secretary};
        \node[attribute,below right of=secretary,node distance=1.6cm,xshift=.5cm] (hours-worked) {hours-worked} edge (secretary);

      \node[isa,at=(employee),shift={(0cm,-0.8cm)}] {ISA} edge (employee) edge (officer) edge (teller) edge (secretary);
    \end{tikzpicture}
    }
    \end{center}
  \end{exampleblock}
\end{frame}