"The use of UML techniques in TRADE has implications for the semantics of these techniques when they are used this way. s and statecharts are used in TRADE to represent software architecture at the essential level, where we can assume perfect technology. This means, for example, that actions do not take time and that all objects perform their tasks in parallel. A first version of such an essential-level semantics is presented elsewhere. This semantics differs from the OMG semantics, in which actions take time, there are several threads of control and one message queue per thread which can receive signals exchanged by objects. The OMG semantics is clearly intended for and appropriate to what I call the implementation architecture. This is called the design model in the Unified Software Development Process. The use of C++ as action language in the executable UML models of Rhapsody confirms this, as does the outline of the executable statechart semantics given by Harel & Gery..."