code: public static String getId(DMNElementReference er) {
          String href = er.getHref();
          return href.startsWith("#") ? href.substring(1) : href;
      }
docs: For the purpose of Compilation, in the DMNModel the DRGElements are stored with their full ID, so an ElementReference might reference in two forms:
  - #id (a local to the model ID)
  - namespace#id (an imported DRGElement ID)
  This method now returns in the first case the proper ID, while leave unchanged in the latter case, in order for the ID to be reconciliable on the DMNModel.