\begin{frame}
  \frametitle{ER Models vs. UML Class Diagrams}

  \begin{goal}{Binary Relationships with Attributes}
  \begin{minipage}{.49\textwidth}
    \begin{center}
    \scalebox{.92}{\small
    \begin{tikzpicture}[every edge/.style={link},node distance=22mm,>=triangle 45,inner sep=.5mm]
      \begin{scope}
        \node[relationship] (R) {R};
        \node (l) [left of=R,entity] {E1}; \draw (R) -- node[above,pos=.4] {role1} (l); 
        \node (r) [right of=R,entity] {E2}; \draw (R) -- node[above,pos=.4] {role2} (r);

        \node [attribute,above left of=R,yshift=2mm] {a1} edge (R);
        \node [attribute,above right of=R,yshift=2mm] {a2} edge (R);
      \end{scope}
    \end{tikzpicture}
    }
    \end{center}
  \end{minipage}
  \begin{minipage}{.49\textwidth}
    \begin{center}
    \quad\quad\begin{tikzpicture}[nodes={xscale=.8}]
    \umlclass[width=5mm]{E1}{ 
      \ldots
    }{} 
    \umlclass[x=3.5cm,width=5mm]{E2}{ 
      \ldots
    }{} 
    \umlassoc[arg1=role1,pos1=0.2,arg2=role2,pos2=.8,name=assoc]{E1}{E2} 
    \umlassocclass[width=5mm,geometry=|-|,x=1.75cm, y=-1.5]{R}{assoc-1}{a1\\a2}{} 
    \end{tikzpicture} 
    \end{center}
  \end{minipage}
  \end{goal}
  
  \begin{itemize}
    \item If the relationship set has attributes, 
          then the name of the relationship set is written in a box 
          together with the attributes of the relation.
    \item The box is then connected using a dashed line to the
          line corresponding to the relationship set.
  \end{itemize}
\end{frame}