draw a DAG with transition labels

I appreciate it if you let me know the most elegant way to draw a DAG such as the followings:

• For better answers you might explain what a DAG is and what specifies it. – Qrrbrbirlbel Apr 18 '13 at 19:09

A possibility but not sure it's the most elegant. I added a little change with (x.45) to draw the edges from the same point like your example. I added also some styles.

 \documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[dot/.style={fill,draw,circle,minimum width=4pt},
arrow style/.style={->,bend left,
line width=1.2pt,shorten >=3pt}]

\path[every node/.style={dot}]
node [label=west:$X$]          (x) {}
+ ( 45:3cm) node [label=east:$T$]          (t) {}
+ (-20:3cm) node [label=south east:$Z$]    (z) {}
+ (-60:3cm) node [label=south:$Y$]         (y) {};

\draw
(x.45)  edge [arrow style] node [auto] {$y$} (y)
edge [arrow style] node [auto] {$z$} (z)
edge [arrow style] node [auto] {$t$} (t);

\end{tikzpicture}
\end{document}


It's possible to get a shorter code but the question is to know if a shorter code is most elegant. Personally I prefer if it's possible to avoid the mix of multiple actions like to draw the nodes first and then to draw the edges.

   \documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}[dot/.style={fill,draw,circle,minimum width=4pt},
arrow style/.style={<-,bend right,line width=1.2pt,
shorten <=3pt,shorten >=3pt}]

\node [dot,label=west:$X$]  (x) {};
\node [dot,label=east:$T$]  (t)  at   (45:3cm)  {}
edge [arrow style] node [auto] {$t$} (x);
\node [dot,label=south east:$Z$]  (z)  at   (-20:3cm)  {}
edge [arrow style] node [auto] {$z$} (x);
\node [dot,label=south:$Y$]  (y)  at   (-60:3cm)  {}
edge [arrow style] node [auto] {$y$} (x);
\end{tikzpicture}
\end{document}


With PSTricks.

\documentclass[preview,border=15pt]{standalone}
\usepackage{pst-eucl}
\psset{shortput=tablr,arrows=->,nodesepB=5pt,dotscale=2,arcangle=45}
\begin{document}
\begin{pspicture}(4,5)
\pstGeonode[PosAngle={0,180,-45,-90}](3,5){T}(0,3){X}(4,2){Z}(2,0){Y}
\ncarc{X}{T}^[tpos=0.3]{$t$}
\ncarc{X}{Z}^[tpos=0.6]{$z$}
\ncarc{X}{Y}^[tpos=0.9]{$y$}
\end{pspicture}
\end{document}