How Sharepoint custom SiteColumn and Database Fields are mapped

In sharepoint you can create a site column which can be used across sites and these articles shows you how they are mapped internally in the sharepoint database

http://msdn2.microsoft.com/en-us/library/aa543680.aspx

http://blogs.msdn.com/andrew_may/archive/2006/06/14/SharePointTermsColumnsFieldsProperties.aspx