Gail-Joon Ahn Badrinath Mohan Seng-Phil Hong Towards secure information sharing using role-based delegation. 42-59 2007 30 J. Network and Computer Applications 1 http://dx.doi.org/10.1016/j.jnca.2005.08.004 db/journals/jnca/jnca30.html#AhnMH07