John Ellson Emden R. Gansner Eleftherios Koutsofios Stephen C. North Gordon Woodhull Graphviz - Open Source Graph Drawing Tools. 483-484 2001 Graph Drawing http://link.springer.de/link/service/series/0558/bibs/2265/22650483.htm db/conf/gd/gd2001.html#EllsonGKNW00