code: private static void convert(unificationXref uni, Model level2)
  	{
  		//We can not simply convert a class, so we need to remove the
          //uni and insert a new relationship xref
  
          //First get all the objects that refers to this uni
          Set<XReferrable> referrables =
  			new HashSet<XReferrable>(uni.isXREFof());
  
          //Create the new relationship xref in the model.
          relationshipXref relationshipXref =
          	level2.addNew(relationshipXref.class, uni.getUri());
  
          //Copy the fields from uni
  		relationshipXref.setCOMMENT(uni.getCOMMENT());
  		relationshipXref.setDB(uni.getDB());
  		relationshipXref.setDB_VERSION(uni.getDB_VERSION());
  		relationshipXref.setID(uni.getID());
  		relationshipXref.setID_VERSION(uni.getID_VERSION());
  		relationshipXref.setRELATIONSHIP_TYPE(
  			"http://www.biopax.org/paxtools/convertedGOUnificationXREF");
  
          //Create a link to the new xref from all the owners.
          for (XReferrable referrable : referrables)
  		{
  			referrable.addXREF(relationshipXref);
  		}
  
          //Remove the references to the old uni
          for (XReferrable referrable : referrables)
          {
              referrable.removeXREF(uni);
          }
          //Now remove it from the model.
          level2.remove(uni);
  
          //We are done!
      }
docs: This method converts the given unification xref to a relationship xref
  @param uni xref to be converted
  @param level2 model containing the xref