File1                                
                  +---------+                                
                  |  Mod1   |                       File1   
                  +---------+                     +---------+
                  |  Mod2   |--+                  |  Mod1   |
                  +---------+  |                  +---------+
                  |  Mod3   |  |   +---------+    |  Mod2   |
                  +---------+  +-->|  PAT    |--->+---------+
                               |   +---------+    | Update2 |
                  +---------+  |                  +---------+
                  | Update2 |--+                  |  Mod3   |
                  +---------+                     +---------+