Peter Ahlbrecht Silke Eckstein Karl Neumann Conceptual Modelling of Mobile Object Systems: Some Language Constructs. 2003 conf/caise/2003fo CAiSE Short Paper Proceedings http://sunsite.informatik.rwth-aachen.de/Publications/CEUR-WS/Vol-74/files/FORUM_23.pdf db/conf/caise/caisefo2003.html#AhlbrechtEN03