The model shown in 88.01 Figure 2 should be considered as a simplified introduction to physical models. It serves to illustrate the definition of some terms. The model was arbitrarily limited to seven levels. That limit has caused some definitions of levels to lose their clarity, as when Site included Region. This section discusses these problems and proposes a crisper physical model without the use of definitions that homogenize necessary concepts into less useful mixtures.

A review of Chapter 6 may help explain what this discussion is about.

The physical model suffers from being in the first part of the standard. Like first impressions, people will read about the physical model and form conceptions of what each of the seven blocks mean before they have been introduced to equipment entities. The physical model is interpreted differently the second time that the standard is read, because the model is not purely physical.

Perhaps the physical model could have been presented as a simple hierarchy with a discussion of the meaning of each layer, with forward references to control concepts where necessary. Some in SP88 thought that forward references in the document were a Very Bad Thing. At least one member of SP88 spent a long time wandering in ignorance because his first impression of the equipment module made it hard to see the need to complicate it with a phase. A simple forward reference to procedural control would have cleared it up.

Figure 14-1 shows a complete...