You create the basic structure of a BSP application in the Web Application Builder (SE80).
Afterwards, you can edit the pages of that application using external tools. This is made possible by a check-out/check-in mechanism. You use external tools primarily for implementing the page layout. It is not possible to edit page parameters and event handlers.
You can use a WebDAV client to perform the following tasks:
Process Flow (See Also Figure Above)
For each new BSP application, the system creates an identically named directory in the MIME Repository.
The pages can then be edited in the WebDAV client.
All imported MIMEs are part of the MIME Repository. By default, these MIMEs are assigned the package of the BSP application.
All new pages are imported as static pages into the MIME Repository. By default, these MIMEs are assigned the package of the BSP application.
Once you have completed these steps, you implement the event handlers, declare the page parameters, and activate and test your BSP application in transaction SE80.