We define four abstract models in common use today for electronic design—electrical, digital gate, digital RTL, and transactional—and discuss the relationships among them. The new low-power model described by IEEE Std 1801-2009 UPF is introduced, and its relationship to the other signal-level models for digital and analog design is defined. We then discuss the connections between the lowpower model and the underlying physical implementation of a chip, elucidating some of the concepts in the low-power model that are missing from the commonly used abstract models. We define extensions to the electrical/RTL boundary model to support application of the low power model in mixed-model simulation. Finally, we recommend extensions to the existing transaction model to reflect the concepts of the low-power model.