Georgia Koutrika Benjamin Bercovitz Robert Ikeda Filip Kaliszan Henry Liou Zahra Mohammadi Zadeh Hector Garcia-Molina Social Systems: Can We Do More Than Just Poke Friends? 2009 CIDR http://www-db.cs.wisc.edu/cidr/cidr2009/Paper_85.pdf conf/cidr/2009 db/conf/cidr/cidr2009.html#KoutrikaBIKLZG09