private function _load()
    {
        if ($this->_simpleXml !== false) {
            return;
        }
        $this->_simpleXml = $this->_loadXml($this->_filename);
        if (empty($this->_simpleXml)) {
            throw new BeanFactoryException(
                'Could not parse: ' . $this->_filename
                . ': ' . $this->_getXmlErrors()
            );
        }
    }