Vassilis Tsiaras Sofia Triantafilou Ioannis G. Tollis Treemaps for Directed Acyclic Graphs. 377-388 2007 conf/gd/2007 Graph Drawing http://dx.doi.org/10.1007/978-3-540-77537-9_37 db/conf/gd/gd2007.html#TsiarasTT07