\documentclass[12pt]{article}
\usepackage{tikz}
\usetikzlibrary{shapes}
\usetikzlibrary{arrows}
\begin{document}
\thispagestyle{empty}
\setlength{\fboxrule}{0.01pt}
\setlength{\fboxsep}{4pt}
\fcolorbox{white}{white}{
\newcommand{\sys}[1]{\emph{#1}}
\begin{tikzpicture}[x = 4cm, y = 1cm]
\tikzstyle positive=[color = black, fill = white];
\tikzstyle negative=[color = white, fill = black];
\tikzstyle entity=[rounded corners, draw, thick];
\tikzstyle process=[ellipse, draw, thick];
\tikzstyle arrow=[-stealth, semithick];
\node (spec) at (0, 3) [entity, positive] {specification tools};
\node (user) at (1, 3) [entity, positive] {user proofs};
\node (spec_user_join) at (0.5, 3) [shape=coordinate] {};
\node (raw) at (0.5, 4) [entity, positive] {raw code equations};
\node (pre) at (1.5, 4) [process, positive] {preprocessing};
\node (eqn) at (2.5, 4) [entity, positive] {code equations};
\node (iml) at (0.5, 0) [entity, positive] {intermediate program};
\node (seri) at (1.5, 0) [process, positive] {serialisation};
\node (SML) at (2.5, 3) [entity, positive] {\sys{SML}};
\node (OCaml) at (2.5, 2) [entity, positive] {\sys{OCaml}};
\node (further) at (2.5, 1) [entity, positive] {(\ldots)};
\node (Haskell) at (2.5, 0) [entity, positive] {\sys{Haskell}};
\draw [semithick] (spec) -- (spec_user_join);
\draw [semithick] (user) -- (spec_user_join);
\draw [-diamond, semithick] (spec_user_join) -- (raw);
\draw [arrow] (raw) -- (pre);
\draw [arrow] (pre) -- (eqn);
\draw [arrow] (eqn) -- node (transl) [process, positive] {translation} (iml);
\draw [arrow] (iml) -- (seri);
\draw [arrow] (seri) -- (SML);
\draw [arrow] (seri) -- (OCaml);
\draw [arrow, dashed] (seri) -- (further);
\draw [arrow] (seri) -- (Haskell);
\end{tikzpicture}
}
\end{document}