Ruoming Jin Yang Xiang Ning Ruan David Fuhry 3-HOP: a high-compression indexing scheme for reachability query. 813-826 2009 SIGMOD Conference http://doi.acm.org/10.1145/1559845.1559930 conf/sigmod/2009 db/conf/sigmod/sigmod2009.html#JinXRF09