Office Open XML (OOXML), sometimes called Open XML, is an XML format that was created by Microsoft as a successor to the binary document formats used through Microsoft Office® version 2003, including .doc, .xls, .ppt. The OOXML format will allow more applications to work with the open documents.
XML stands for eXtensible Markup Language, which refers to a simple text format. That it is extensible simply means that it allows designers to customize the tags within the language. One of the aims of this language is to help share structured data among multiple people.
An OOXML file contains a collection of XML files compressed into a single file, which can be created and modified with Microsoft Office®. The files created in Office 2007 are not proprietary to Microsoft Office® as the OOXML format was standardized by the International Standards Organization (ISO) in April of 2008. This version of the format is the most recent, the original specification was standardized in December of 2006 by Ecma International, a non-profit private standardization group.
Bringing OOXML to Microsoft Office 2007® is one of the ways Microsoft is becoming more open and less reliant on closed proprietary software. Open formats such as XML and OOXML allow more applications from other vendors to interact with documents more easily. This will eventually reduce the amount of file corruption that can happen when files are exchanged. The format is new in the release of Office 2007, but as Microsoft expands its installation base of the software, the format will grow in popularity.
Being an XML based format, OOXML can allow the individual pieces of a word document or power point presentation to be stored separately. These parts are compressed using a subset of the ZIP compression scheme to create file type when office documents are saved. When a user opens an OOXML file, the application handles the compressed collection of files but displays them as a single file. In the long term, it is conceivable that certain third party applications may be able to access the parts of the compressed OOXML file that they need and disregard the rest.
The new format created by Microsoft is not entirely related to the OpenOffice.org XML which is a deprecated version of this format. The latest release of OpenOffice.org, version 3.0 can open OOXML files that are created by MS Office 2007, but it cannot currently save documents in that format. As the format grows the free OpenOffice will likely be able to write to the Microsoft Office 2007 OOXML standard format, allowing documents to be modified by users of either application suite.