,-----------.   ,---------------------.
   ,-----------.  |==bb system|   |==transaction manager|
   |==aa system|  |-----------|   |---------------------|
   |-----------|  | big system|   | manages transactions|
   `-----------'  |           |   |                     |
                  `-----------'   `---------------------'
                                                         
                                                         
,-----------------.                                      
|==account master |  ,---------------------------.       
|-----------------|  |==enter label for <u:red>Xm|       
| manages accounts|  |---------------------------|       
|                 |  `---------------------------'       
`-----------------'