TheSDLandMSC(SAM)workshop, heldeverytwoyears, providesanopend- cussionarenaontopicsrelatedtothemodellingandanalysisofreactivesystems, distributed systems, and real-time systems (e.g., telecommunications, auto- tive, aerospace, and Web-based applications). The SAM workshop is a place for intensive discussions enabling the unfolding of ideas for the future devel- ment and application of SDL and MSC, and of related languages: ASN.1, eODL, TTCN, UML, and URN. The fourth instance of this workshop was held at the University of Ottawa, Canada, from June 1 to June 4, 2004 (http:...