\begin{frame} \frametitle{Cycles in the Connection Graph} \begin{goal}{} The connection graph may contain \emph{cycles}, which makes the selection of the ``right path'' more difficult (and error-prone). \end{goal} \medskip \begin{exampleblock}{} A database of course enrolments, could have the cycle: \smallskip \begin{center} \begin{tikzpicture}[n/.style={rectangle,rounded corners=1mm,draw=black,fill=cblue!30,inner sep=1mm}] \node (S) [n] {\sql{Students}}; \node (T) [n,right of=S,node distance=35mm,yshift=7mm] {\sql{Teaching Assistants}}; \node (E) [n,right of=S,node distance=35mm,yshift=-7mm] {\sql{Enrolments}}; \node (C) [n,right of=T,node distance=35mm,yshift=-7mm] {\sql{Courses}}; \draw (S) to (T); \draw (S) to (E); \draw (C) to (T); \draw (C) to (E); \end{tikzpicture}\vspace{-1ex} \end{center} \smallskip \end{exampleblock} \end{frame}