Dong-Hong Xu Yong Qi Di Hou Gong-Zhen Wang Ying Chen An Improved Calculus for Secure Dynamic Services Composition. 686-691 2008 COMPSAC http://doi.ieeecomputersociety.org/10.1109/COMPSAC.2008.18 conf/compsac/2008 db/conf/compsac/compsac2008.html#XuQHWC08