OpenOffice.org/OASIS File Format

OpenDocument (OASIS Open Document Format for Office Application) is the native file format of OpenOffice.org. It is an Open Standard file format, meaning it is freely available and implementable without the need for paying a royalty fee. A common OpenDocument Format file is a plain XML file (Extensible Markup Language), usually contained inside a ZIP archive.

Brief History of OpenDocument Format
OASIS (Organization for the Advancement of Structured Information Standards) takes the base for the OpenDocument standard from OpenOffice's native file format, which originates from Sun's proprietary office suite StarOffice file format. Later OpenOffice became the first and the de facto standard for implementation of OpenDocument.

Competing Formats

 * Microsoft's OpenXML file format, which is largely hailed as an incompatible competitor to the OpenDocument Format. This standard is implemented on the new Microsoft Office 2007, and updates would be available to support this format on previous versions of Microsoft Office. On the most current release, OpenOffice.org does natively support Microsoft's OpenXML format.
 * Microsoft's binary proprietary format, which is Microsoft Office's native file format prior to Microsoft Office 2007. OpenOffice.org could open and save to this format, however the conversion process could take some time for really large and complex files. OpenOffice.org is reported to be capable to open old files created by previous version of Microsoft Office that even the newer Microsoft Office Suites cannot.
 * Microsoft Works format - OpenOffice.org can open documents in Works' format, however saving is not supported.

OpenOffice.org/Estrutura de um documento