This Part of ISO/IEC 29500 specifies a set of conventions that are used by Office Open XML documents to define the structure and functionality of a package in terms of a package model and a physical model. The package model is a package abstraction that holds a collection of parts. The parts are composed, processed, and persisted according to a set of rules. Parts can have relationships to other parts or external resources, and the package as a whole can have relationships to parts it contains or to external resources. The package model specifies how the parts of a package are named and related. Parts have content types and are uniquely identified using the well-defined naming rules provided in this Part of ISO/IEC 29500. The physical mapping defines the mapping of the components of the package model to the features of a specific physical format, namely a ZIP archive.