http://www.research.att.com/sw/tools/graphviz/
http://www.loveruby.net/%7Eaamine/ja/readingcode.html
http://homepage3.nifty.com/kaku-chan/graphviz/
http://reddog.s35.xrea.com/wiki/Graphviz.html
http://skazami.web.infoseek.co.jp/tools/Graphviz_Doxygen.htm
http://muffin.cias.osakafu-u.ac.jp/~matumoto/unix/graphviz.html