Johan Bollen Herbert Van de Sompel Lyudmila Balakireva Ryan Chute A ranking and exploration service based on large-scale usage data. 444 2008 JCDL http://doi.acm.org/10.1145/1378889.1378989 conf/jcdl/2008 db/conf/jcdl/jcdl2008.html#BollenSBC08