Brian Gallagher Hanghang Tong Tina Eliassi-Rad Christos Faloutsos Using ghost edges for classification in sparsely labeled networks. 256-264 2008 KDD http://doi.acm.org/10.1145/1401890.1401925 conf/kdd/2008 db/conf/kdd/kdd2008.html#GallagherTEF08