We present a revision of the hierarchical, modular Discrete Event System Specification (DEVS) modeling formalism. The revision distinguishes between transition collisions and ordinary external events in the external transition function of DEVS models. Such separation enables us to extend the modeling capability of the collisions. The revision also does away with the necessity for tie-breaking of simultaneously scheduled events, as embodied in the select function. The latter is replaced by a

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... -defined and consistent formal construct that allows all transitions to be simultaneously activated. The revision provides a modeler wit h both conceptual and parallel-execution benefits.