How to make a reference to others elements name ?

Question

Hi, i have a xsd element like this :

• A
• sub element 1
  
  • sub element 2
    ...
  • sub element N

This A element is retun by a webservice.
I'm looking for a way to tell in the request to the webservice that i want the element A
with NOT the full list but with somes of his sub elements.

For example : just A with sub element 1 and 3.

The first idea is to send to the webservice a list of elements names to retrieve.

But theres no way than for the xml validator in the server side that intercept my request to tell if the Request is xml-valid(we are using spring)
Is there a way to make a reference to some elements with their names in order to preserve th possibility to be xml valid ?

Thanks in advance for your answer. I really appreciate.And excuse me for my poor english. it is not my mother tongue.