Spatio-temporal XACML: the expansion of XACML for access control. - Ki Young Lee; Aleum Kim; Ye Eun Jeon; Jeong-Joon Kim; Yong Soon Im; Gyoo-Seok Choi; Sang-Bong Park; Yun Sik Lim; Jeong Jin Kang (Int. J. Secur. Networks, 2015)