\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{shapes.geometric}
\usetikzlibrary{arrows}

\begin{document}

\begin{tikzpicture}
  \begin{scope}[minimum width=8em,minimum height=3ex]
  \node[draw,rectangle] (eql) at (0,0) {\texttt{eql-specializer}};
  \node[draw,rectangle] (class) at (1,2) {\texttt{class}};
  \node[draw,rectangle] (specializer) at (0.5,6) {\texttt{specializer}};
  \node[draw,ellipse] (argument) at (7,2) {\textit{argument}};

  \node[draw,red,ellipse] (generalizer) at (7,4) {\textit{\color{red}generalizer}};
  \node[draw,red,rectangle] (genspec) at (2,4) {\texttt{\color{red}gen.-spec.}};
  \end{scope}

  \draw[->,>=open triangle 60] (eql.168) |- (specializer);
  \draw[->,>=open triangle 60] (class.160) -- (class.160 |- specializer.south);
  \draw[->,>=open triangle 60,red] (genspec.150) -- (genspec.150 |- specializer.south);

  \draw[dashed] (argument.south) |- node[right,near start] {\texttt{eql}} node[below,near end] {\texttt{eql-specializer-object}} (eql.east);
  \draw[dashed] (argument.west) -- node[below] {\texttt{subtypep}} node[above] {\texttt{class-of}} (class.east);
  \draw[red] (argument.north) -- node[right] {\texttt{\color{red}generalizer-of}} (generalizer.south);
  \draw[red] (generalizer.west) -- node[above] (sagp) {\texttt{\color{red}s-a-g-p}} (genspec.east);
  \node (specaccgenp) at (6,5.5) {\texttt{\footnotesize{\color{red}specializer-accepts-generalizer-p}}};
  \draw[red,dotted] (sagp) -- (specaccgenp);

\end{tikzpicture}

\end{document}