\begin{frame}
  \frametitle{Examples}
  
  \begin{goal}{}
    Functional dependencies between \emph{attributes of a relationship} always violate BCNF.
  \end{goal}
  
  \begin{exampleblock}{Violation of BCNF on the ER level}
    \begin{tcenter}
      \scalebox{.9}{
      \begin{tikzpicture}[every edge/.style={link}]
        \node[entity] (customer) {Customers};
        \node[entity,xshift=70mm] (product) {Products};
        
        \node[attribute] [at=(customer),shift={(-1cm,1cm)}] {\key{customerNr}} edge (customer);
        \node[attribute] [at=(product),shift={(1cm,1cm)}] {\key{productNr}} edge (product);

        \node[relationship] at($(customer)!.5!(product)$) (order) {orders}
          edge node [pos=.7,above] {$0..*$} (customer)
          edge node [pos=.7,above] {$0..*$} (product);

        \node[attribute] [at=(order),shift={(0cm,1.4cm)}] {orderNr} edge (order);
        \node[attribute] [at=(order),shift={(0cm,-1.4cm)}] {date} edge (order);
      \end{tikzpicture}
      }  
    \end{tcenter}
    \pause
    The FD $\text{orderNr} \to \text{date}$ violates BCNF.
    \begin{itemize}
      \item 
      The key of the table corresponding to the relationship set
      ``orders'' consists of the attributes customerNr, productNr.
    \end{itemize}
    \pause
    \smallskip
    
    This shows that the concept ``order'' is an independent entity.
  \end{exampleblock}
\end{frame}