\documentclass[12pt]{article}

 \usepackage{pgf}

 \usepackage{pgflibraryshapes}

 \usepackage{tikz}

 \begin{document}

 \begin{tikzpicture}[x = 4.2cm, y = 1cm]

   \tikzstyle entity=[rounded corners, draw, thick, color = black, fill = white];

   \tikzstyle process=[ellipse, draw, thick, color = green, fill = white];

   \tikzstyle process_arrow=[->, semithick, color = green];

   \node (HOL) at (0, 4) [style=entity] {Isabelle/HOL theory};

   \node (eqn) at (2, 2) [style=entity] {code equations};

   \node (iml) at (2, 0) [style=entity] {intermediate language};

   \node (seri) at (1, 0) [style=process] {serialisation};

   \node (SML) at (0, 3) [style=entity] {SML};

   \node (OCaml) at (0, 2) [style=entity] {OCaml};

   \node (further) at (0, 1) [style=entity] {\ldots};

   \node (Haskell) at (0, 0) [style=entity] {Haskell};

   \draw [style=process_arrow] (HOL) .. controls (2, 4) ..

     node [style=process, near start] {selection}

     node [style=process, near end] {preprocessing}

     (eqn);

   \draw [style=process_arrow] (eqn) -- node (transl) [style=process] {translation} (iml);

   \draw [style=process_arrow] (iml) -- (seri);

   \draw [style=process_arrow] (seri) -- (SML);

   \draw [style=process_arrow] (seri) -- (OCaml);

   \draw [style=process_arrow, dashed] (seri) -- (further);

   \draw [style=process_arrow] (seri) -- (Haskell);

 \end{tikzpicture}

 \end{document}