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Office Open XML (OOXML) is a family of XML-based office document formats and a multipart standard—not a single application or one XML file. It defines how word-processing, spreadsheet, and presentation documents are represented and how their parts are packaged for exchange.
What Office Open XML means
ECMA-376 defines OOXML’s vocabularies, document representation, and packaging, and sets requirements for software that produces or consumes OOXML documents. Ecma describes the standard as covering word-processing, spreadsheet, and presentation formats. Its primary markup languages are WordprocessingML (WML), SpreadsheetML (SML), and PresentationML (PML). Ecma’s current overview also identifies charts among the kinds of content represented. Ecma’s ECMA-376 standard page and its Office Open XML formats topic description provide the formal scope.
OOXML is therefore a standard and a related family of formats, rather than the name of a particular office program. A document can include material from more than one of the primary markup languages, along with supporting markup languages. Ecma TC45’s overview describes this relationship.
How an OOXML file is organized
An OOXML file is not simply a standalone XML document. It is a package made up of parts, each containing a byte stream. The markup languages describe document content and semantics; the Open Packaging Conventions (OPC) define how the parts are organized into a package. ZIP is a recommended physical implementation of OPC, not the definition of OOXML’s markup.
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This distinction matters when inspecting or handling an OOXML file: the document’s content is distributed across package parts, while packaging rules describe how those parts fit together. The standard’s overview explains the package model and OPC in more detail in Ecma TC45’s Office Open XML overview.
ECMA-376 and ISO/IEC 29500
ECMA-376 is titled “Office Open XML file formats” and is associated with ISO/IEC 29500. Ecma lists ECMA-376’s fifth edition as December 2021, but the parts do not all share the same edition date or adoption status:
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| ECMA-376 part | Subject | Fifth-edition date listed by Ecma |
|---|---|---|
| Part 1 | Fundamentals and Markup Language Reference | December 2016 |
| Part 2 | Open Packaging Conventions | December 2021 |
| Part 3 | Markup Compatibility and Extensibility | December 2015 |
| Part 4 | Transitional Migration Features | December 2016 |
Ecma’s standard page says that only Part 2 was adopted in the last edition of ECMA-376. These dates and the adoption qualification are listed on Ecma’s ECMA-376 page; they should not be read as one shared publication date for all four parts.
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Why the standard exists
OOXML’s interoperability goal is that a conforming producer and a conforming consumer can exchange a document and agree on its semantics. In other words, the standard aims to make the meaning of a document intelligible across implementations that follow its requirements; it does not mean every application will necessarily render every document identically in every circumstance.
Ecma TC45 describes the initial aim as enabling implementation across a wide range of tools and platforms, with interoperability between office productivity applications and line-of-business systems. Responsibility for managing OOXML work has moved to ISO/IEC JTC 1/SC 34/WG 4, with Ecma TC45 assisting WG 4 on ongoing maintenance and evolution. See Ecma’s TC45 committee scope and the Ecma TC45 overview.
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