code: @Override
      public Object readValue(final Attribute _attribute,
                              final List<Object> _objectList)
      {
          final List<String> ret = new ArrayList<String>();
          for (final Object object : _objectList) {
              final StringBuilder oid = new StringBuilder();
              if (object instanceof Object[]) {
                  final Object[] temp = (Object[]) object;
                  oid.append(temp[0]).append(".").append(temp[1]);
              } else {
                  oid.append(_attribute.getParentId()).append(".").append(object);
              }
              ret.add(oid.toString());
          }
          return _objectList.size() > 0 ? (ret.size() > 1 ? ret : ret.get(0)) : null;
      }
docs: The oid (object id) is the type id, than a point and the id itself. If in
  the attribute the attribute has no defined type id SQL column name, the
  type from the attribute is used (this means, the type itself is not
  derived and has no childs).
  
  @param _attribute    related attribute which is read
  @param _objectList   list of objects from the eFaps Database
  @return Object as needed for eFaps