This Part (the Open Packaging Conventions specification) 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 defines 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 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 guidelines provided in this Open Packaging specification.

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.

This Open Packaging Conventions specification also describes certain features that might be supported in a package, including core properties for package metadata, a thumbnail for graphical representation of a package, and digital signatures of package contents.

Because this Standard will continue to evolve, packages are designed to accommodate extensions and support compatibility goals in a limited way. The versioning and extensibility mechanisms described in Part 5: "Markup Compatibility and Extensibility" support compatibility between software systems based on different versions of this Standard while allowing package creators to make use of new or proprietary features.

This Open Packaging Conventions specification specifies requirements for package implementers, producers, and consumers.

In all subsequent uses, the term "this specification" shall refer to the content of this Part.