ARFS
Why use OpenDocument and not Office Open XML?

The current "standards": the DOC/XLS/PPT formats

Usage

The "de facto" standard for documents is today Microsoft's DOC/XLS/PPT formats, used for text documents, spreadsheets and presentations. The extensions of these files are well known (".doc", ".xls", ".ppt"), and many people exchange documents in this formats.

Problems

These formats have many problems, one of the most important is that they are "binary" formats, meaning that they are unreadable without an appropriate program that understands it. There has also been a big problem for the free software community because specification of these formats (a specification is a document that describes how the format works) has never been made available by Microsoft. So free software developers had to understand how Microsoft's binary formats worked by analizing documents, which was a lot of work. Moreover, Microsoft could just change the format the way they wanted, so free software developers had to keep looking at Microsoft's changes in Microsoft Office.

Today this format, although very bad and not an approved standard, is widely used and is implemented in many free software office suites like OpenOffice.org and KOffice. This support has been improved by years of difficult work.

OpenDocument, the modern and open standard

A better format

On the other hand, OpenOffice.org, a free software office suite, has used an XML-based format for years. Files created with it had extensions like ".sxw", ".sxc", ".sxi". In fact these files were just ZIP files with XML files in it. XML files are text with tags that add structure to it. That means that if you have an SXW file from OpenOffice.org but you don't have OpenOffice.org installed, you can still unzip the file and read directly the XML code.

Making a new standard

The OASIS (Organization for the Advancement of Structured Information Standards) then developed a new standard based on the OpenOffice.org one: OpenDocument. OpenDocument files have extensions like ".odt", ".ods", ".odp". This new standard uses the same idea (XML in ZIP files) and was very much the same. But the new idea was to publish a standard that other office suites could implement. OpenOffice.org would then just becomes one of many OpenDocument implementations.

OpenDocument becomes an ISO standard

On May 3, 2006, OpenDocument was approved as an ISO (International Organization for Standards) standard (ISO/IEC 26300:2006). It was finally published on November 30, 2006 by the ISO.

Implementing OpenDocument

OpenOffice.org of course switched to OpenDocument, which is the default format from OpenOffice.org Version 2.0 (released in October 20, 2005). The KOffice free software office suite dropped their own format to use OpenDocument instead, which is now the default format in this suite. This means for example that documents created with KOffice can then be modified using OpenOffice.org (and vice-versa). Other programs that have implemented OpenDocument include Google Docs, and IBM Lotus Symphony.

Microsoft's Office Open XML format

Brief history

At the same time, Microsoft developped a new format, based on the same idea (XML files in ZIP), but different, and made it the default format in Microsoft Office 2007. For examples, Microsoft Word documents now have a ".docx" extension. This new format, Office Open XML (nothing to do with "OpenOffice.org XML" which is the ancestor of OpenDocument!), sometimes simply called OpenXML or OOXML, was approved by the ECMA. It was finally approved, although controversial, by the ISO on April 2, 2008.

The problem with Office Open XML

Office Open XML basically does the same thing as OpenDocument. They don't have exactly the same features but there is none of them that has really more features. Some of the problems with Office Open XML are:

There is already an ISO standard for documents (OpenDocument). Having 2 standards to do the same thing is a bad idea because it is more work for developers and is not benefic to users.
There is a risk that someone that fully implements Office Open XML could be sued by Microsoft for patent violations.
Office Open XML has many technical problems, which are one of the most important reasons why the ISO rejected it.
Office Open XML documents integrate binary data from the old DOC/XLS/PPT formats, for which there is no specifiation available.
Office Open XML does not reuse existing standards like SVG and MathML like OpenDocument does, Office Open XML uses DrawingML, VML and Office Math ML instead, so it "reinvents the wheel". This makes it more difficult to implement because new algorithms must be written specially for Office Open XML.
Office Open XML specification is 5946 pages long, which shows it is a complicated standard, while OpenDocument achieves the same goals in a simpler way (OpenDocument specification is 706 pages long).
Office Open XML was designed only by Microsoft, whereas OpenDocument was designed in an open process.

So, to summerize, Office Open XML is good...

For Microsoft, because they can reuse the old work they have already done in Microsoft Office.
For Microsoft, beacuse it will be more difficult for competitors to implement Office Open XML than OpenDocument (although it will still be less difficult than implementing old Microsoft DOC/XLS/PPT formats).

And OpenDocument is good...

For all others developers of office suites, because it is less complicated to implement OpenDocument, and because as it reuses a lot of already defined standards, developers can use already written libraries (they do not need to reinvent the wheel).
For users, because they can use OpenDocument without the risk of vendor lock-in i.e. they will never become dependant on a specific program to read their documents. For example, OpenOffice.org and KOffice are free software office suites that use the OpenDocument format by default, and that can be downloaded at no cost.

ARFS Why use OpenDocument and not Office Open XML?