The problem is that i can set a value of an xfa Form data field '/process_data/inForm/object/data/xdp/datasets/data/FormXML/myField' to a vaue like "myValue", but if i need to get it ie: i use "x+y" service and i map myField to a variable when i debug i see that the variable is empty, but myfield is filled on the form and i can see this when i view the form.
any suggestion ?
Yes, this is definitly possible.
If you use a set value you should be able to put the content of /process_data/inForm/object/data/xdp/datasets/data/FormXML/myField into a string variable.
Can you provide the expression that you are placing in the SetValue QPAC? Make sure that you are setting the value first then assigning it to your variable.