It is recognized that there is no general methodology for writing correct timed specifications. Timed systems differ from untimed systms in that their runs are composed of alternating discrete transitions and time steps. When describing systems as the parallel composition of independent timed components,it is not in general easy to preserve this property, given that time progress must be synchronous inall compo0nents. We have shown in previous papers, that a source of problems is the fact that usually composition of timed formalisms, such as process algebras or timed automata, is defined by composing independently time steps and discrete (untimed) transitions.
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