Example: Fault tree

% A simple fault tree
% Author: Zhang Long, Mail: zhangloong[at]gmail.com
%\def\pgfsysdriver{pgfsys-dvipdfm.def}
\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{shapes.gates.logic.US,trees,positioning,arrows}
\begin{document}
\begin{tikzpicture}[
% Gates and symbols style
    and/.style={and gate US,thick,draw,fill=red!60,rotate=90,
		anchor=east,xshift=-1mm},
    or/.style={or gate US,thick,draw,fill=blue!60,rotate=90,
		anchor=east,xshift=-1mm},
    be/.style={circle,thick,draw,fill=green!60,anchor=north,
		minimum width=0.7cm},
    tr/.style={buffer gate US,thick,draw,fill=purple!60,rotate=90,
		anchor=east,minimum width=0.8cm},
% Label style
    label distance=3mm,
    every label/.style={blue},
% Event style
    event/.style={rectangle,thick,draw,fill=yellow!20,text width=2cm,
		text centered,font=\sffamily,anchor=north},
% Children and edges style
    edge from parent/.style={very thick,draw=black!70},
    edge from parent path={(\tikzparentnode.south) -- ++(0,-1.05cm)
			-| (\tikzchildnode.north)},
    level 1/.style={sibling distance=7cm,level distance=1.4cm,
			growth parent anchor=south,nodes=event},
    level 2/.style={sibling distance=7cm},
    level 3/.style={sibling distance=6cm},
    level 4/.style={sibling distance=3cm}
%%  For compatability with PGF CVS add the absolute option:
%   absolute
    ]
%% Draw events and edges
    \node (g1) [event] {No flow to receiver}
	     child{node (g2) {No flow from Component B}   
	     	child {node (g3) {No flow into Component B}
	     	   child {node (g4) {No flow from Component A1}
	     	      child {node (t1) {No flow from source1}}
	     	      child {node (b2) {Component A1 blocks flow}}
			}
	     	   child {node (g5) {No flow from Component A2}
	     	      child {node (t2) {No flow from source2}}
	     	      child {node (b3) {Component A2 blocks flow}}
			}
		   }
	     	child {node (b1) {Component B blocks flow}}
		};
%% Place gates and other symbols
%% In the CVS version of PGF labels are placed differently than in PGF 2.0
%% To render them correctly replace '-20' with 'right' and add the 'absolute'
%% option to the tikzpicture environment. The absolute option makes the 
%% node labels ignore the rotation of the parent node. 
   \node [or]	at (g2.south)	[label=-20:G02]	{};
   \node [and]	at (g3.south)	[label=-20:G03]	{};
   \node [or]	at (g4.south)	[label=-20:G04]	{};
   \node [or]	at (g5.south)	[label=-20:G05]	{};
   \node [be]	at (b1.south)	[label=below:B01]	{};
   \node [be]	at (b2.south)	[label=below:B02]	{};
   \node [be]	at (b3.south)	[label=below:B03]	{};
   \node [tr]	at (t1.south)	[label=below:T01]	{};
   \node [tr]	at (t2.south)	[label=below:T02]	{};
%% Draw system flow diagram
   \begin{scope}[xshift=-7.5cm,yshift=-5cm,very thick,
		node distance=1.6cm,on grid,>=stealth',
		block/.style={rectangle,draw,fill=cyan!20},
		comp/.style={circle,draw,fill=orange!40}]
   \node [block] (re)					{Receiver};
   \node [comp]	 (cb)	[above=of re]			{B}  edge [->] (re);
   \node [comp]	 (ca1)	[above=of cb,xshift=-0.8cm]	{A1} edge [->] (cb);
   \node [comp]	 (ca2)	[right=of ca1]			{A2} edge [->] (cb);
   \node [block] (s1)	[above=of ca1]		{Source1} edge [->] (ca1);
   \node [block] (s2)	[right=of s1]		{Source2} edge [->] (ca2);
   \end{scope}
\end{tikzpicture}
\end{document}