Open Packaging Conventions

The open packaging convention (OPC) is a file packaging format created by Microsoft for storing a combination of XML and non-XML files that together form a single entity like an XPS document in a single compressed file container. This format combines the advantages of leaving the independant file entities embedded in the document intact and having a vastly reduced fileformat compared to normal XML storage files.

Usage

Both the XML Paper Specification (XPS) and Office Open XML (OOXML) use Open Packaging Conventions, which provide a profile of the common ZIP format. As well as XML data and document files the ZIP package can also include other text and binary files in formats such as PNG, BMP, AVI, PDF, RTF or even an already packaged ODF file. OPC also defines some naming conventions and an indirection method to allow position-indepence of binary and XML files in the ZIP archive.

Open Packaging Convention files can be opened using common ZIP utilities. Open source libraries in .NET and Java are available for using Open Packaging Conventions. The Open Packaging Convention is specified in Part 2 of Ecma 376 (131 pages) but is not dependent on other parts of Office Open XML. The Open Packaging Convention specifies the details of the ZIP format because ZIP has not actually been specified by any international standard previously, but has widespread community and developer acceptance."