我想通过ISBN查找Amazon的图书，然后将图书信息保存在自己的数据库

以下是我写的代码
$time=gmdate("Y-m-d\TH%3\Ai%3\As\Z");
$accessKey="AKIAIIYGPBDDFTN4CVHA"; // Access Key
$isbnAmazon=$isbnNum;
$myhash=hash_hmac("SHA256","GET\nwebservices.amazon.com\n/onca/xml\nAWSAccessKeyId=$accessKey&ItemId=$isbnAmazon&Operation=ItemLookup&ResponseGroup=Images&Service=AWSECommerceService&Timestamp=$time","Vg2tM8mqVNxviF44B2zpy/C84Jgj7NdssBhy7QfL",true);//Vg2tM8mqVNxviF44B2zpy/C84Jgj7NdssBhy7QfL is the Secret Access Key
$myhash=base64_encode($myhash);
$myhash=str_replace("=","%3D",$myhash);
$myhash=str_replace("+","%2B",$myhash);
$httpRequest="http://webservices.amazon.com/onca/xml?AWSAccessKeyId=$accessKey&ItemId=$isbnAmazon&Operation=ItemLookup&ResponseGroup=Images&Service=AWSECommerceService&Timestamp=$time&Signature=$myhash";
$qureStr=$httpRequest;
//end of new way $rss =  simplexml_load_file($qureStr);   // have waring
if($rss->Items->Request->Errors->Error->Code==null)
{
$author=(string)$rss->Items->Item->ItemAttributes->Author;
$title = (string)$rss->Items->Item->ItemAttributes->Title;
$publisher=(string)$rss->Items->Item->ItemAttributes->Manufacturer;
$backurl=(string)$rss->Items->Item->DetailPageURL;
$linkurl=(string)$rss->Items->Item->MediumImage->URL;
}