Work on the OMG RFP for a Uml Action Semantics is available at:

http://uml.simware.com ''BrokenLink -- Is this page still relevant? First and last edit on this page was August 27, 1999.''

I dunno. But http://www.kc.com/as_site/home.html seems like a suitable link (2005-01-01).

See also UnifiedModelingLanguage