public function findEntryUrl($identifierref, \DOMNodeList $resources)
    {
        foreach ($resources as $resource) {
            $identifier = $resource->attributes->getNamedItem('identifier');

            if (!is_null($identifier)) {
                $identifierValue = $identifier->nodeValue;

                if ($identifierValue === $identifierref) {
                    $href = $resource->attributes->getNamedItem('href');

                    if (is_null($href)) {
                        throw new InvalidScormArchiveException('sco_resource_without_href_message');
                    }

                    return $href->nodeValue;
                }
            }
        }
        throw new InvalidScormArchiveException('sco_without_resource_message');
    }