Test data is information you use like set "Value" , 
Parameter in datatable , this test data 

Test case is define condition that will check expected 
behaviour of application like checkpoint

Test Case is nothing but Raw form of actions which we need 
to perform.
Test case converted to a standard format(XL sheet or XML 
file)which an automated tool understands is called test data

And about Object Hierarchy it is just the way the 
application is developed.
Parent object and child objects
window(objectname1).menu(objectname2).select

Here objectname1 is parent object which specifies a window.
and object2 is child object which is a menu in that window.

So,here hierarchy means without knowing the objectname1 
that is a window we cant sleect the objectname2 that is a 
menu.

testdata is dataprovided to execute the test case...whereas 
test case is a criteria to execute the scriprt.

Object hierarchy is the path to find out in which window of 
appliction the object is present.

If something wrong pls let me know - 
test_professional7@yahoo.com