The mapping of part names to the names of items in the physical package uses an intermediate logical item name abstraction. This logical item name abstraction allows package implementers to manipulate physical data items consistently regardless of whether those data items can be mapped to parts or not or whether the package is laid out with simple ordering or interleaved ordering. See §9.1.4 for interleaving details.
example:
Figure 9–1 illustrates the relationship between part names, logical item names, and physical package item names.
