protected function _getAttr($oc, $attr)
    {
        $oc = strtolower($oc);
        if (key_exists($oc, $this->_objectClasses) && key_exists($attr, $this->_objectClasses[$oc])) {
            return $this->_objectClasses[$oc][$attr];
        } elseif (key_exists($oc, $this->_oids) &&
                $this->_oids[$oc]['type'] == 'objectclass' &&
                key_exists($attr, $this->_oids[$oc])) {
            return $this->_oids[$oc][$attr];
        } else {
            return PEAR::raiseError("Could not find $attr attributes for $oc ");
        }
    }