Suppose I installed one module, let says sale module. Inside this sale module, there is one method, let says create_order.

Then, I installed one community module, let says sale_com_module which inherit the sale module and overwrite the method create_order.

Finally, I created and installed my custom module which also inherit sale module and overwrite the method create_order.

How did OpenERP knows which create_order method to be used if all three modules have been installed?