The definitions of IEEE Std 1076.1 allow users to build simulation models of physical components and subsystems that may belong to multiple energy domains (electrical, fluidic, mechanical, etc.). Such models are built upon sets of properties that are specific to each energy domain and encapsulated in socalled natures. IEEE Std 1076.1 provides a mechanism to define natures, but intentionally does not predefine any standard set of natures as it is expected that this would be done in a subsequent IEEE standard project. The definition of a standard set of natures is crucial to make possible the reuse and exchange of models written in VHDL 1076.1 within and among vendors.