Hamdan Dammag Nimal Nissanke A Mathematical Framework for Safecharts. 620-640 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2885&spage=620 2003 conf/icfem/2003 ICFEM db/conf/icfem/icfem2003.html#DammagN03