\documentclass{ppex}
\nonstopmode
\usepackage {pstricks,pst-node}
\pagestyle{empty}

\begin{document}
\ResetPreambleCommands
\ReadyForTheFray
\usepackage {pstricks,pst-node}
\psset{framearc=.4}
\begin{psmatrix}[colsep=3]
 \pnode{A}&\psframebox{Waiting} & \psframebox{Calculating}
 \ncline[arrows=->]{1,1}{1,2}
 \psset{offset=-.1}
 \ncline[arrows=->]{1,2}{1,3}\naput{{\scriptsize TRIGGER/activated}}
 \psset{offset=.1}
 \ncline[arrows=<-]{1,2}{1,3}\nbput{{\scriptsize [4,11]/finished}}
\end{psmatrix}
\end{document}