Diyaa-Addein Atiya Steve King Jim Woodcock A Circus Semantics for Ravenscar Protected Objects. 617-635 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2805&spage=617 2003 conf/fm/2003 FME db/conf/fm/fme2003.html#AtiyaKW03