Update ReferenceData.xid.xml to provide source URI in the RefPointSet definition.

@@ -132,7 +132,12 @@
     </struct>
     </struct>
 
 
     <struct name="RefPointSet">
     <struct name="RefPointSet">
-      <comment>a set of reference points</comment>
+      <comment>A set of reference points with source information.</comment>
+      
+      <elem name="source" type="Tensor.uri" multiplicity="1">        
+        <comment>URI identifies the source of the information provided.</comment>      
+      </elem>
+            
       <elem name="refpoints" type="RefPoint" multiplicity="0..*"  polymorphic="true"/>
       <elem name="refpoints" type="RefPoint" multiplicity="0..*"  polymorphic="true"/>
       
       
     </struct>
     </struct>