William Browuer Saurabh Kataria Sujatha Das Prasenjit Mitra C. Lee Giles Segregating and extracting overlapping data points in two-dimensional plots. 276-279 2008 JCDL http://doi.acm.org/10.1145/1378889.1378936 conf/jcdl/2008 db/conf/jcdl/jcdl2008.html#BrowuerKDMG08