@InCollection{	  pretschner.ea:policy:2008,
  author	= {A. Pretschner and F. Sch{\"u}tz and C. Schaefer and T.
		  Walter},
  booktitle	= {4th Intl. Workshop on Security and Trust Management},
  language	= {USenglish},
  month		= 06,
  title		= {Policy Evolution in Distributed Usage Control},
  year		= 2008,
  user		= {pretscha}
}