Michael Backes Markus Dürmuth Rainer Steinwandt An Algebra for Composing Enterprise Privacy Policies. 33-52 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3193&spage=33 2004 conf/esorics/2004 ESORICS db/conf/esorics/esorics2004.html#BackesDS04