\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}