Generating File Names
Here, the function modules are stored that generate a file name when IDocs are exchanged through a port with the type "File". These function modules are displayed as a list of possible entries (F4) when you create a file
port. The standard system already contains some examples of such function modules. You can store your own function modules here.
Activities
You maintain the function modules in the ALE Customizing transaction 
SALE
Communication
File Name Generation Function Module (WE55).
.
Caution
The function module must return a directory and file in a character string. Like the standard function modules, it can copy the directory from the port description, but this is not mandatory.
End of the caution.