With Office 2007, Microsoft decided to change the default application formats from old, proprietary, closed formats (DOC, XLS, PPT) to new, open and standardized XML formats (DOCX, XLSX and PPTX).  New formats share some similarities with old Office XML formats (WordML, SpreadsheetML) and some similarities with competing OpenOffice.org OpenDocument formats, but there are many differences.  Since new formats will be the default in Office 2007 and Microsoft Office is the most predominant office suite, these formats are destined to be popular and you will probably have to deal with them sooner or later.

This article will explain the basics of Open XML file format and specifically XLSX format, the new format for Excel 2007.  Presented is a demo application which writes/reads tabular data to/from XLSX files.  The application is written in C# using Visual Studio 2005.  Created XLSX files can be opened using Excel 2007 Beta (we used build 12.0.3820.1003).