\begin{figure}[!h]
\label{xaf_facade}
\begin{center}

\begin{psmatrix}[rowsep=0.6,colsep=0.6]
[name=TRex] \psbox{3cm}{TRex API} 	& [name=AST]	\psbox{4.5cm}{TRex \ttcn{} AST} \\
\pnode{x} 					& [name=XML]	\psbox{4.5cm}{XML representation of the TRex \ttcn{} AST} \\
\pnode{x} 					& [name=Facade]	\psbox{4.5cm}{XQuery Facade Layer} \\
\pnode{x}					& [name=Smell]	\psbox{4.5cm}{XQuery Smell Detection}

\ncline{*->}{AST}{XML}
\ncline{o->}{Facade}{XML}
\ncline{o->}{Smell}{Facade}
\ncline{o->}{TRex}{AST}
\ncbar[angle=180]{o->}{Facade}{TRex}
\end{psmatrix}

\end{center}
\caption{Central position of the XQuery facade layer module}
\end{figure}