protected function prepareMetadata(array $category)
    {

        // initialize the metadata
        $metadata = array();

        // query whether or not, the passed category IS the root category
        if ($this->isRootCategory($category)) {
            return;
        }

        // if not, set the category ID in the metadata
        $metadata[UrlRewriteObserver::CATEGORY_ID] = (integer) $category[MemberNames::ENTITY_ID];

        // return the metadata
        return $metadata;
    }