title: Excel file and program structure
body: <p>I need to know for a school project how Excel work. Precisely I need to know what kind of structure is behind an Excel file and how the Excel program work with this file.</p>
  
  <p>I know Excel is a Microsoft propriety and it' s not Open Source so I know I can' t find too much on this argument... But everything that can help me to understand how excel work it' s useful.</p>
  
  <p>If I could not find something about Excel I will try to take a look at Open Office or Open Document format. So even some information about this will be real useful.</p>
  
  <p>Thanks to all</p>