\begin{frame}
  \frametitle{Cardinalities affect the ER Design}
  
  \begin{exampleblock}{}
    \begin{center}
      \scalebox{.92}{
      \begin{tikzpicture}[every edge/.style={link}]
        \node[entity] (customer) {customer};
        \node[attribute] (id) [above left of=customer,node distance=1.7cm,shift={(-2mm,-3mm)}] {\key{id}} edge (customer);
        \node[attribute] (name) [above of=customer,node distance=1.3cm] {name} edge (customer);
        \node[attribute] (street) [left of=customer,node distance=2.1cm] {street} edge (customer);
        \node[attribute] (city) [below left of=customer,node distance=1.7cm] {city} edge (customer);

        \node[entity,right of=customer, node distance=6cm] (account) {account};
        \node[attribute] (account-number) [above of=account,node distance=1.2cm] {\key{account-number}} edge (account);
        \node[attribute] (balance) [below right of=account,node distance=1.7cm,xshift=-5mm] {balance} edge (account);

        \node[relationship] (does) at ($(customer)!.5!(account)$) {depositor} edge (customer) edge (account);
      \end{tikzpicture}}
    \end{center}
    \medskip
    
    Assume that we want to record the date of the last access of a customer to an account.
    We call this attribute \textit{access-date}.
    \medskip
    \pause
    
    If the relation from customer to account is \emph{many-to-many}:
    \begin{itemize}
      \item then \textit{access-date} must be an attribute of \textit{depositor} 
    \end{itemize} 

    If the relation from customer to account is \emph{one-to-many}:
    \begin{itemize}
      \item then \textit{access-date} can be an attribute of \textit{account} 
    \end{itemize} 
  \end{exampleblock}
\end{frame}