I am confused now. i created the xml files, the back end c# code properties and all relationship between files, now i need to call a wcf service to return a list of different colunms? how to do that? i have been trying so many things...

select a.proj_id,a.manager_empid,b.activity_id,b.last_dml_dttm,c.descr,d.user_name
,d.first_name || ' ' || d.last_name as Name
from table a,
table b,
table c,
table d
where a.proj_id=:project_id
and a.proj_id=b.proj_id
and a.proj_id=c.proj_id
and a.manager_empid=d.user_id
and b.last_dml_dttm =(select max(last_dml_dttm) from project_activity where proj_id=:project_id);

i have no luck, where to start... do i use the objects to build that query and i can i build a query like that?

It is possible, if you define [DataContract] for all objects in the query.