Madalina Croitoru Liang Xiao 0002 David Dupplaw Paul H. Lewis Expressive security policy rules using Layered Conceptual Graphs. 209-216 2008 21 Knowl.-Based Syst. 3 http://dx.doi.org/10.1016/j.knosys.2007.11.006 db/journals/kbs/kbs21.html#CroitoruXDL08