With the soon-to-be released next version of Microsoft® Office (currently code-named “Office 12”), there will be new default file formats for Microsoft Word, PowerPoint®, and Excel®. These new formats, called the Microsoft Office Open XML Formats, will open up a whole new world to Office developers. By default, Office documents will be open and accessible, as they will use standard ZIP and XML technologies with full documentation made available under a royalty-free license. These technologies are an improvement on the existing XML formats that shipped with Microsoft Office 2003 Editions, but those existing Office 2003 XML Reference Schemas can be used today to implement solutions that work with the document data and they provide a great way to gain an understanding of what developing with the new default formats will entail.
Introduction to Excel XML.