Office Open XML

Office Open XML (also referred to as OOXML, OpenXML, or Open XML) is a file format for representing spreadsheets, charts, presentations and word processing documents. An Office Open XML document file contains mainly XML based files compressed within a zip package.

The Office Open XML format specification has been approved as a free and open Ecma International standard. A newer improved version is approved as an ISO/IEC standard.²³⁴⁵⁶⁷⁸

Microsoft originally developed the specification as a successor to its earlier binary and Office 2003 XML file formats. The specification was later handed over to Ecma International to be developed as the Ecma 376 standard, under the stewardship of Ecma International Technical Committee TC45. Ecma 376 was published in December 2006⁹ and can be freely downloaded from Ecma International.¹⁰

An amended version of the format, ISO/IEC DIS 29500 (Draft International Standard 29500), 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 2008.¹¹

The current stage in the standardization process of ISO/IEC IS 29500 is "International Standard under publication".¹² The official designation of the international standard is: ISO/IEC IS 29500, Information technology – Office Open XML formats.

Starting with Microsoft Office 2007, the Office Open XML file formats have become the default file format of Microsoft Office, the currently market-leading office suite.¹³¹⁴ Microsoft Office 14 will be the first version to implement the ISO/IEC IS 29500 compliant version of Office Open XML.¹⁵

Background

Prior to the 2007 edition, the core applications of the Microsoft Office software suite (primarily Word, Excel, and PowerPoint) by default stored their data in binary files. Historically, these files were difficult for other applications to interoperate with, due to the lack of publicly available information and royalty-free access to the format specifications. More recently, Microsoft has offered these binary format specifications under a royalty-free covenant not to sue as part of its Open Specification Promise.¹⁶¹⁷ While a level of support for the binary formats had been achieved by some applications, full interoperability remained elusive.

In 2000, Microsoft released an initial version of an XML-based format for Excel, which was incorporated in Office XP. In 2002, a new file format for Microsoft Word followed.¹⁸ The Excel and Word formats – known as the Office 2003 XML formats – were later incorporated into the 2003 release of Microsoft Office.

In May 2004, governments and the European Union recommended to Microsoft that they publish and standardize their XML Office formats through a standardization organization.¹⁹¹⁸ Microsoft announced in November 2005 that it would standardize the new version of their XML-based formats through Ecma, as "Ecma Office Open XML".²⁰

File format and structure

Office Open XML uses a file package conforming to the Open Packaging Convention. This format uses mechanisms from the ZIP file format and contains the individual files that form the basis of the document. In addition to Office markup, the package can also include embedded files such as images, videos, or other documents.

Document markup languages

An Office Open XML file may contain several documents encoded in specialized markup languages corresponding to applications within the Microsoft Office product line. Office Open XML defines multiple vocabularies using 27 namespaces and 89 schema modules.

In addition to the above markup languages custom XML schemas can be used to extend Office Open XML.

The XML Schema of Office Open XML emphasizes reducing load time and improving parsing speed. In a test with applications current in April 2007, XML based office documents were slower to load than binary formats.²¹ To enhance performance, Office Open XML uses very short element names for common elements and spreadsheets save dates as index numbers (starting from 1899 or from 1904). In order to be systematic and generic, Office Open XML typically uses separate child elements for data and metadata (element names ending in Pr for properties) rather than using multiple attributes, which allows structured properties. Office Open XML does not use mixed content but uses elements to put a series of text runs (element name r) into paragraphs (element name p). The result is terse and highly nested in contrast to HTML, for example, which is fairly flat, designed for humans to write in text editors and is more congenial for humans to read.

Office MathML (OMML)

Office Math Markup Language is a mathematical markup language which can be embedded in WordprocessingML, with intrinsic support for including word processing markup like revision markings,²² footnotes, comments, images and elaborate formatting and styles.²³ The OMML format is different from the World Wide Web Consortium (W3C) MathML recommendation that does not support those office features, but is partially compatible²⁴ through relatively simple XSL Transformations.

DrawingML

DrawingML is the vector graphics markup language used in Office Open XML documents. Its major features are the graphics rendering of text elements, graphical vector based shape elements, graphical tables and charts.

The DrawingML table is the third table model in Office Open XML (next to the table models in WordprocessingML and SpreadsheetML) and is optimized for graphical effects and its main use is in presentations created with PresentationML markup. DrawingML contains graphics effects (like shadows and reflection) that can be used on the different graphical elements that are used in DrawingML. In DrawingML you can also create 3d effects, for instance to show the different graphical elements through a flexible camera viewpoint. It is possible to create separate DrawingML theme parts in an Office Open XML package. These themes can then be applied to graphical elements throughout the Office Open XML package.²⁵

DrawingML is unrelated to the other vector graphics formats such as SVG. These can be converted to DrawingML to include natively in an Office Open XML document. This is a different approach to that of the OpenDocument format, which uses a subset of SVG, and includes vector graphics as separate files.

Container structure

Office Open XML documents are stored in Open Packaging Convention (OPC) packages, which are ZIP files containing XML and other data files, along with a specification of the relationships between them.²⁶ Depending on the type of the document, the packages have different internal directory structures and names. An application will use the relationships files to locate individual sections (files), with each having accompanying metadata, in particular MIME metadata.

A basic package contains an XML file called [Content_Types].xml at the root, along with three directories: _rels, docProps, and a directory specific for the document type (for example, in a .docx word processing package, there would be a word directory). The word directory contains the document.xml file which is the core content of the document.

Relationships

Relationship files in Office Open XML

As such, images referenced in the document can be found in the relationship file by looking for all relationships that are of type http://schemas.microsoft.com/office/2006/relationships/image. To change the used image, edit the relationship.

Hyperlink relations

In this example, the Uniform Resource Locator (URL) is represented by "rId2". The actual URL is in the accompanying relationships file, located by the corresponding "rId2" item. Linked images, templates, and other items are referenced in the same way.

Embedded or linked media file relations

This is the reference to the image file. All references are managed via relationships. For example, a document.xml has a relationship to the image. There is a _rels directory in the same directory as document.xml, inside _rels is a file called document.xml.rels. In this file there will be a relationship definition that contains type, ID and location. The ID is the referenced ID used in the XML document. The type will be a reference schema definition for the media type and the location will be an internal location within the ZIP package or an external location defined with a URL.

Document properties

Office Open XML uses the Dublin Core Metadata Element Set and DCMI Metadata Terms to store document properties. Dublin Core is a standard for cross-domain information resource description and is defined in ISO 15836:2003.

Core properties

An example document properties file (docProps/core.xml) that uses Dublin Core metadata, is:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:coreProperties xmlns:cp="http://schemas.openxmlformats.org/package/2006/metadata/core-properties"
  xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:dcterms="http://purl.org/dc/terms/"
  xmlns:dcmitype="http://purl.org/dc/dcmitype/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <dc:title>Office Open XML</dc:title>
  <dc:subject>File format and structure</dc:subject>
  <dc:creator>Wikipedia</dc:creator>
  <cp:keywords>Office Open XML, Metadata, Dublin Core</cp:keywords>
  <dc:description>Office Open XML uses ISO 15836:2003</dc:description>
  <cp:lastModifiedBy>Wikipedia</cp:lastModifiedBy>
  <cp:revision>1</cp:revision>
  <dcterms:created xsi:type="dcterms:W3CDTF">2008-06-19T20:00:00Z</dcterms:created>
  <dcterms:modified xsi:type="dcterms:W3CDTF">2008-06-19T20:42:00Z</dcterms:modified>
  <cp:category>Document file format</cp:category>
  <cp:contentStatus>Final</cp:contentStatus>
</cp:coreProperties>

Structure of the standard

To aid the reader's understanding, the Office Open XML specification contains both normative material and informative material.

ISO/IEC 29500:2008

The ISO/IEC standard is structured into four parts, each of which are independent standards.²⁷^{citation needed}

The standard specifies six levels of document and application conformance, strict and transitional for each of WordprocessingML, PresentationML and SpreadsheetML. The standard also specifies applications descriptions of base and full.

ECMA 376:2006

The ECMA standard is structured in five parts to meet the needs of different audiences.¹⁰

Licensing

Reasonable and Non Discriminatory

Ecma International provides specifications that "can be freely copied by all interested parties without restrictions".²⁸ Under the Ecma code of conduct in patent matters, participating and approving member organisations are required to make available their patent rights on a Reasonable and Non Discriminatory (RAND) basis. While making patent rights available on a RAND basis is considered a common minimum patent condition for a standard, international standardization has a clear preference for royalty-free patent licensing. That is why Microsoft, a main contributor to the standard, provided a Covenant Not to Sue²⁹ for its patent licensing. The covenant received a mixed reception, with some (like the Groklaw blog) identifying problems³⁰ and others (such as Lawrence Rosen, an attorney and lecturer at Stanford Law School) endorsing it.³¹

Open Specification Promise

subject to certain restrictions. Office Open XML can therefore be used under the Covenant Not to Sue or the Open Specification Promise.

The Open Specification Promise was included in documents submitted to ISO in support of the Ecma 376 fast track submission.³³ Ecma International asserted that, "The OSP enables both open source and commercial software to implement [the specification]."³⁴

In support of the licensing arrangements Microsoft commissioned an analysis from the London legal firm Baker & McKenzie.³⁵

Several standards and OSS licensing experts expressed support in 2006 of the OSP. A 2006 article in Cover Pages quotes Lawrence Rosen, an attorney and lecturer at Stanford Law School, as saying,

In 2006³⁷, Mark Webbink; a lawyer and member of the board of the Software Freedom Law Center, and former employee of Linux vendor Red Hat; has said,

On March 12, 2008 the Software Freedom Law Center, which provides services to protect and advance free software and open source software, has warned of problems with the Open Specification Promise as it relates to Office Open XML and the GNU General Public License (GPL).⁴⁰ In a published analysis of the promise it states that⁴¹

Microsoft amended the OSP FAQ to specifically assure GPL license users that the open licensing of its covered formats through the Open Specification Promise applies to users of the GPL license when implementing covered implementations:

Legal experts and academics have confirmed that the licensing is similar to the licensing terms offered by IBM, and to a lesser extent Sun and Adobe on their Office formats but warned that ambiguous legal jargon contained in Microsoft's Open Specification Promise, although understood in the terminology of the specialist patent and intellectual property law community, makes it hard for small developers to determine with certainty that Microsoft will not be entitled to sue them for using OOXML. They criticize Microsoft for not explicitly defining which parts of its 6000 page OOXML specification contains intellectual property. The OSP has never been tested in a court of law regarding intellectual property rights, and the OSP does not name which court or jurisdiction a dispute will be heard in. David Vaile, executive director of the Cyberspace Law and Policy Centre at the University of New South Wales, acknowledges that the Microsoft approach to its Open Specification Promise is similar although not identical to other approaches used by IBM, and to a lesser extent Adobe and Sun, and that these represent a substantial advance on the past practice of negotiating long case-by-case agreements.⁴⁴

Standardization

Office Open XML is currently an Ecma standard (Ecma-376, approved on 7 December 2006). Ecma 376 was created using as a basis a new version of the Microsoft Office 2003 XML file format, donated by Microsoft, which was being created for Microsoft Office 12.

The specification entered fast-track standardization within ISO/IEC as DIS 29500 (Draft International Standard 29500).⁴⁵ In a September 2007 vote by ISO/IEC member bodies, the draft text was not approved as an international standard. A ballot resolution process in March 2008 amended the text.

On April 2, 2008, ISO and IEC officially stated that the DIS 29500 had been approved for acceptance as an ISO/IEC Standard, pending any appeals.¹¹ In accordance with the JTC 1 directives the Project Editor created a new version with the final text within a month after the BRM, to be published as ISO/IEC 29500. After review and corrections this text has been distributed to the members of SC34.⁴⁶

On May 21st, 2008, Microsoft announced that it will be an active participant in the future evolution of the Office Open XML standard.⁴⁷

In october 2008 ISO/IEC committee JTC1/SC34 (Document Description and Processing Languages) created a working group for maintenance of the ISO/IEC 29500 standard within ISO/IEC. ⁴⁸

Application support

Ecma 376 implementations

The current Ecma 376 specification is supported in several office suites from various vendors.

Filters and converters

Other products

Planned and beta software

ISO/IEC 29500 implementations

Microsoft has stated that Microsoft Office 14 will be the first version of Microsoft Office to support ISO/IEC 29500, though no release date has been announced.⁴⁷

On July 28, 2008 Murray Sargent, a software development engineer in the Microsoft Office team confirmed that Word 2007 will have a service pack release that enables it to read and write ISO standard OOXML files.¹⁰⁰

Microsoft, whose products currently only support the Ecma 376 standard version of Office Open XML, has committed to using the ISO/IEC 29500 standard in their products¹⁰¹ and has also committed to participate in the maintenance of this standard.

In a Zdnet article Alex Brown, leader of the ISO/IEC group in charge of deciding maintenance processes for any ISO/IEC 29500 Standard, stated

On March 13, 2008 Doug Mahugh, a Senior Product Manager at Microsoft specializing in Office client interoperability and the Open XML file formats confirmed that version 1.0 of the Open XML Format SDK

Implementations

Criticism

The ODF Alliance UK Action Group says that with OpenDocument an ISO-standard for Office files already exists and that two competing standards are against the very concept of a standard.¹¹² Further, they argue that the Office Open XML file-format is heavily based on Microsoft's own Office applications and is thus not vendor-neutral, and that it has inconsistencies with existing ISO standards such as time and date formats and color codes.¹¹²

Specific criticism

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