Is that right if I treat web service in this way?

Question

The web service is the main logic of a program. The web service is the back-end, and other programs / UI is the front-end. The communication between back-end and front-end is communicated via XML.

Answer 1

It depends on your reasons for having the web service. Is there any reason for the main logic to be isolated behind a web service? Why can you not have that logic bundled together with the front end (properly decoupled and architected of course). You are going to have a performance hit every time you communicate with the web service, so you don't want to be hiding too much logic behind it unless you have a compelling reason to do so.