Jimmy's first blog post (http://blogs.msdn.com/teams_wit_tools/archive/2007/04/30/understanding-the-tfs-cube.aspx) on the Team blog explains the structure of the TFS cube! He covers four perspectives* in great detail.

*"Perspectives" is a great feature in SQL Server 2005 (Enterprise Edition) that groups the subset of related cube entities, such as measure groups and dimensions, into views; it makes it easier to navigate the cube. You can learn more about perspectives here: http://msdn2.microsoft.com/en-us/library/ms175338.aspx.