code: public List<Instance> getInstances4Attribute(final String _attributeName)
          throws EFapsException
      {
          final OneSelect oneselect = this.attr2OneSelect.get(_attributeName);
          return oneselect == null ? null : oneselect.getInstances();
      }
docs: Method to get the instance for an <code>_attributeName</code>.
  
  @param _attributeName name of the attribute
  @return list of instance
  @throws EFapsException on error