A taxonomy of event time representations

Terms such as "simulated time", "simulation time", "virtual time", "logical time", and "real time" appear throughout the modeling and simulation literature as a means of describing the timing, ordering, and/or processing of events. Unfortunately, this vocabulary can become a source of confusion due to subtle inconsistencies in how the terms are interpreted. Here we categorize mathematical representations of event times, review their formal properties such as causal consistency and causal characterization, identify formal relationships among the representations, and present a taxonomy to clarify the proper meanings of the most common notions of time in a simulation context. A thorough look at the various event time representations suggests new research opportunities, such as the repurposing of distributed computing techniques for debugging both parallel and sequential discrete event simulations.