Physical Mapping Guidelines
Whereas the package model defines a package abstraction, an instance of a package must be based on a physical representation. A physical package format is a particular physical representation of the package contents in a file.
Many physical package formats have features that partially match the packaging model components. In defining mappings from the package model to a physical package format, it is advisable to take advantage of any similarities in capabilities between the package model and the physical package medium while using layers of mapping to provide additional capabilities not inherently present in the physical package medium.
example: : Some physical package formats store parts as individual files in a file system, in which case it is advantageous to map many part names directly to identical physical file names.
Designers of physical package formats face some common mapping problems.
example: : Associating arbitrary content types with parts and supporting part interleaving Package implementers might use the common mapping solutions defined in this Open Packaging specification. [O2.3]