Qi Li Mingwei Xu Xinwen Zhang Towards a Group-Based RBAC Model and Decentralized User-Role Administration. 441-446 2008 ICDCS Workshops http://dx.doi.org/10.1109/ICDCS.Workshops.2008.26 conf/icdcsw/2008 db/conf/icdcsw/icdcsw2008.html#LiXZ08a