protected function parseRelationship($node)
    {
        $rel = array();

        $x = preg_replace('/\(.*?\)/', '', $node->text('marc:subfield[@code="w"]'));
        if (!empty($x)) {
            $rel['id'] = $x;
        }

        $x = $node->text('marc:subfield[@code="t"]');
        if (!empty($x)) {
            $rel['title'] = $x;
        }

        $x = $node->text('marc:subfield[@code="g"]');
        if (!empty($x)) {
            $rel['parts'] = $x;
        }

        $x = $node->text('marc:subfield[@code="x"]');
        if (!empty($x)) {
            $rel['issn'] = $x;
        }

        $x = $node->text('marc:subfield[@code="z"]');
        if (!empty($x)) {
            $rel['isbn'] = $x;
        }

        return $rel;
    }