Office Open XML (also informally known as OOXML or Microsoft Open XML (MOX)) is a zipped, XML-based file format developed by Microsoft for representing spreadsheets, charts, presentations and word processing documents. The format was initially standardized by Ecma (as ECMA-376), and by the ISO and IEC (as ISO/IEC 29500) in later versions.
Microsoft Office 2010 provides read support for ECMA-376, read/write support for ISO/IEC 29500 Transitional, and read support for ISO/IEC 29500 Strict. Microsoft Office 2013 and Microsoft Office 2016 additionally support both reading and writing of ISO/IEC 29500 Strict. While Office 2013 and onward have full read/write support for ISO/IEC 29500 Strict, Microsoft has not yet implemented the strict non-transitional, or original standard, as the default file format yet due to remaining interoperability concerns.
In 2000, Microsoft released an initial version of an XML-based format for Microsoft Excel, which was incorporated in Office XP. In 2002, a new file format for Microsoft Word followed. The Excel and Word formats—known as the Microsoft Office XML formats—were later incorporated into the 2003 release of Microsoft Office.
Main article: Standardization of Office Open XML
This standard was then fast-tracked in the Joint Technical Committee 1 of ISO and IEC. After initially failing to pass, an amended version of the format received the necessary votes for approval as an ISO/IEC Standard as the result of a JTC 1 fast-tracking standardization process that concluded in April 2008. The resulting four-part International Standard (designated ISO/IEC 29500:2008) was published in November 2008 and can be downloaded from the ITTF. A technically equivalent set of texts is published by Ecma as ECMA-376 Office Open XML File Formats—2nd edition (December 2008); they can be downloaded from their web site.
The same InfoWorld article reported that IBM (which supports the ODF format) threatened to leave standards bodies that it said allow dominant corporations like Microsoft to wield undue influence. The article further says that Microsoft was accused of co-opting the standardization process by leaning on countries to ensure that it got enough votes at the ISO for Office Open XML to pass, although it does not specify exactly who accused Microsoft.
Microsoft, the main contributor to the standard, provided a covenant not to sue for its patent licensing. The covenant received a mixed reception, with some like the Groklaw blog criticizing it, and others such as Lawrence Rosen, (an attorney and lecturer at Stanford Law School), endorsing it.
Microsoft irrevocably promises not to assert any Microsoft Necessary Claims against you for making, using, selling, offering for sale, importing or distributing any implementation to the extent it conforms to a Covered Specification […]
This is limited to applications which do not deviate from the ISO/IEC 29500:2008 or Ecma-376 standard and to parties that do not "file, maintain or voluntarily participate in a patent infringement lawsuit against a Microsoft implementation of such Covered Specification". The Open Specification Promise was included in documents submitted to ISO/IEC in support of the ECMA-376 fast-track submission. Ecma International asserted that, "The OSP enables both open source and commercial software to implement [the specification]".
The Office Open XML specification exists in a number of versions.
The ECMA standard is structured in five parts to meet the needs of different audiences.
Later versions of the ECMA-376 standard are aligned and technically equivalent to the corresponding ISO standard.
A technically equivalent set of texts is also published by Ecma as ECMA-376 2nd edition (2008).
The standard specifies two levels of document & application conformance, strict and transitional, for each of WordprocessingML, PresentationML and SpreadsheetML, and also specifies applications' descriptions of base and full.
The intent of the changes from ECMA-376 1st Edition to ISO/IEC 29500:2008 was that a valid ECMA-376 document would also be a valid ISO 29500 Transitional document; however, at least one change introduced at the BRM—refusing to allow further values for xsd:boolean—had the effect of breaking backwards-compatibility for most documents. A fix for this had been suggested to ISO/IEC JTC1/SC34/WG4, and was approved in June 2009 as a recommendation for the first revision to Office Open XML.
Applications capable of reading documents compliant to ECMA-376 Edition 1 would regard ISO/IEC 29500-4 Transitional documents containing ISO 8601 dates as corrupt.
Main article: List of software that supports Office Open XML
Starting with Microsoft Office 2007, the Office Open XML file formats have become the default file format of Microsoft Office. However, due to the changes introduced in the Office Open XML standard, Office 2007 is not wholly in compliance with ISO/IEC 29500:2008. Office 2010 includes support for opening documents of the ISO/IEC 29500:2008-compliant version of Office Open XML, but it can only save documents conforming to the transitional, not the strict, schemas of the specification. Note that the intent of the ISO/IEC is to allow the removal of the transitional variant from the ISO/IEC 29500 standard.
The ability to read and write Office Open XML format is, however, not limited to Microsoft Office; other office products are also able to read & write this format:
XLSXfiles in its word processor & spreadsheet applications.
Other office products that offer import support for the Office Open XML formats include:
Ecma Standards and Technical Reports are made available to all interested persons or organizations, free of charge and licensing restrictions
the ability to open password-protected Word, Excel, and PowerPoint files
Import of password protected Microsoft Office XML files
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