code: private Pair<String, String> extractLinkValue(TableDefinition tableDef, String colName) {
          if (colName.length() < 3 || colName.charAt(0) != '~') {
              return null;
          }
          
          // A '/' should separate the field name and object ID value. Example: ~foo/xyz
          int slashInx = 1;
          while (slashInx < colName.length() && colName.charAt(slashInx) != '/') {
              slashInx++;
          }
          if (slashInx >= colName.length()) {
              return null;
          }
          String fieldName = colName.substring(1, slashInx);
          String objID = colName.substring(slashInx + 1);
          return Pair.create(fieldName, objID);
      }
docs: target object ID as a Pair<String, String>