Subash Shankar Sinan Asa Formal Semantics of UML with Real-Time Constructs. 60-75 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2863&spage=60 2003 conf/uml/2003 UML db/conf/uml/uml2003.html#ShankarA03