Inside the Excel XML File Format

Excel 2007 builds on its history of XML support with a new file format called the Office Open XML format. This new format improves file and data management, data recovery, and interoperability. Any application that supports XML can access and work with information in an Excel 2007 workbook. This means it is now possible to work with your Excel data in systems outside of Microsoft Office products as long as they provide XML support.

Additionally, security concerns are reduced, since you now have your Excel data in what is essentially a text file. This allows data to pass through firewalls without difficulty.

The new XML file format is based on the compressed ZIP file format specification. Each ZIP container is made up of numerous XML files containing what Microsoft refers to as "parts." While most parts are XML files describing workbook data, metadata, and document information, non-XML files like binary files representing images or OLE objects may also be included in the ZIP file. There are also relationship parts that describe the relationships between parts, thus providing the structure for the workbook file. The parts are the content of the workbook and the relationships detail how the content parts fit together.

Figure 3-20 shows the Open XML format's file container.

Open XML Format's File Container

Document Properties

Custom-Defined XML

Charts

Embedded Code/Macros

Images, Video, Sound Files

WordML, SpreadsheetML, etc.

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Figure 3-20. Open XML format's file container

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