Process algebraic specification languages, i.e., CSP, CCS, LOTOS, etc., are semantically founded in the notion of interleaved traces of events. Unfortunately such traces are inadequate when the dimension of "real" time is considered since a totally ordered trace cannot model two or more time-consuming events overlapping in time. As a first step towards solving this problem, it is explained how, through a simple notational device, conventional traces can be augmented to retain causal event

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... onships. As a concrete illustration, a constructive definition of Basic LOTOS is given in terms of partially ordered traces. The resultant properties are discussed and their applicability outlined. An implementation of these concepts, as a trace generator, is described.