My code:
\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{vietnam}
\usepackage{amsmath,amssymb,mathptmx}
\usepackage{pstricks,pst-node} % required package
\usepackage{auto-pst-pdf}
\begin{document}
\begin{pspicture}
\psmatrix[,colsep=1.5cm]
& [mnode=circle] X \\
[mnode=oval] ABCD & \psframebox[framearc=.3]{E}
\endpsmatrix
\psset{nodesep=3pt,nrot=:U}
\ncline{1,2}{2,1}
\nbput{abcd}
\ncline{<-}{1,2}{2,2}
\ncput*{ch}
\ncline[linestyle=dotted]{2,1}{2,2}
\nbput{dcba}
\end{pspicture}
\end{document}
How to rotate "abcd" like "above"? Is there another way?
\nbput->\naput.
The result as the following: