Qihua Wang Hongxia Jin Ninghui Li Usable Access Control in Collaborative Environments: Authorization Based on People-Tagging. 268-284 2009 ESORICS http://dx.doi.org/10.1007/978-3-642-04444-1_17 conf/esorics/2009 db/conf/esorics/esorics2009.html#WangJL09