V-Model

\begin{figure}
  \center
  \begin{tikzpicture}[
    nd/.style={draw, rounded corners, minimum height=1cm, minimum width=3cm, fill=white},
    line/.style={thick},
  ]
    \node (req)    [nd] at ( 0, 0 * -1.25) {Requirements};
    \node (spec)   [nd] at ( 1, 1 * -1.25) {Specification};
    \node (arch)   [nd] at ( 2, 2 * -1.25) {Architectural Design};
    \node (mod)    [nd] at ( 3, 3 * -1.25) {Module Design};
    \node (imp)    [nd] at ( 5, 4 * -1.25) {Implementation};
    \node (unit)   [nd] at ( 7, 3 * -1.25) {Unit Testing};
    \node (int)    [nd] at ( 8, 2 * -1.25) {Integration Testing};
    \node (sys)    [nd] at ( 9, 1 * -1.25) {System Testing};
    \node (accept) [nd] at (10, 0 * -1.25) {Acceptance Testing};

    \draw [->, line] (req) -- (spec);
    \draw [->, line] (spec) -- (arch);
    \draw [->, line] (arch) -- (mod);
    \draw [->, line] (mod) -- (imp);
    \draw [->, line] (imp) -- (unit);
    \draw [->, line] (unit) -- (int);
    \draw [->, line] (int) -- (sys);
    \draw [->, line] (sys) -- (accept);
  \end{tikzpicture}
  \caption{The V-Model.}
  \label{fig:v-model}
\end{figure}