Office Open XML

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Office Open XML (OOXML) is an XML-based file format used for representing word processing documents, spreadsheets, and presentations. It is conceptually similar to ODF in many respects, though a lot of the details differ. OOXML was created by Microsoft and has been used as the default format in all versions of Office since 2007. It has been published as a standard as both ISO 29500 and ECMA-376.

The official specifications for OOXML, which come in four parts, are available here (search for "29500"):

There are two versions of OOXML - "Strict" and "Transitional". The former is a subset of the latter, and excludes certain legacy features that the latter retains to facilitate conversion from the older binary formats. Currently, OOXML Transitional is the only variant in widespread use; OOXML Strict is only fully supported in Office 2013 for Windows, though Office 2010 contains the ability to read (but not write) Strict documents.

OOXML documents of both variants use the .docx, .xlsx, and .pptx extensions for word processing documents, spreadsheets, and presentations, respectively. Thus it is easy to tell the difference between an OOXML file and the older MS Office binary format, which uses .doc, .xls, and .ppt.

The following pages describe various aspects of the standard:


A new import filter is currently (as of May 2014) in development. Its design and implementation is described on this page. The legacy importer and exporter is described here.

The new OOXML import framework is currently in the design stage. Development is about to begin.


What Who Status
Create new main/ooxml/ module and setup initial build files Andre In progress
  • Collect a list of the relevant schema files.
  • Determine legal status of OOXML schemas.
  • Setup map of different specification variants and applications.
  • Write the schema parser
DSL parser
  • Finialize DSL design
  • Implement DSL parser
Implement OOXML parser generator
Migrate existing PresentationML import

File Format

The file format is described by several documents:

There are three main markup languages (MLs) for the three main applications:

  • WordprocessingML
  • SpreadsheetML
  • PresentationML

Markup languages that are shared by all applications are

  • DrawingML
  • VML (for legacy files)

OOXML files are, similar to ODF files, ZIP containers with one entry per XML stream. OOXML calls these entries parts.


A new framework for the import of OOXML documents is designed to make the import code based on this framework easy to read and easy to develop. In a compile time pre-processing step the OOXML schema files are read and turned into the OOXML parser skeleton. A domain specific language (DSL) can then be used to provide the implementation for specific elements (complex types) of the OOXML format.

Details can be found on the OOXML Framework page.

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