Ravi S. Sandhu Jaehong Park Usage Control: A Vision for Next Generation Access Control. 17-31 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2776&spage=17 2003 conf/mmmacns/2003 MMM-ACNS db/conf/mmmacns/mmmacns2003.html#SandhuP03