result to the file `.git/HEAD`, so that we can always see what the
last committed state was.
+Here is an ASCII art by Jon Loeliger that illustrates how
+various pieces fit together.
+
+------------
+
+ commit-tree
+ commit obj
+ +----+
+ | |
+ | |
+ V V
+ +-----------+
+ | Object DB |
+ | Backing |
+ | Store |
+ +-----------+
+ ^
+ write-tree | |
+ tree obj | |
+ | | read-tree
+ | | tree obj
+ V
+ +-----------+
+ | Index |
+ | "cache" |
+ +-----------+
+ update-index ^
+ blob obj | |
+ | |
+ checkout-index -u | | checkout-index
+ stat | | blob obj
+ V
+ +-----------+
+ | Working |
+ | Directory |
+ +-----------+
+
+------------
+
+
6) Examining the data
~~~~~~~~~~~~~~~~~~~~~