XQuery usecase "R" Q5

Hi, 

I have a comment about the xquery solution and expected result to the
UseCase "R" Q5. First, the expected result is not quite right, because we
should also list the item that doesn't have any bid which is itemno 1008 in
this case. For this matter, the previous version of Use Cases is right. So
the expected result should be:
<result> 
<jones_bike> <itemno> 1001 </itemno> <description> Red Bicycle
</description> <high_bid> 55 </high_bid> <bidder> Mary Doe </bidder>
</jones_bike> <jones_bike> <itemno> 1008 </itemno> <description> Broken
Bicycle </description> </jones_bike> 
</result> 
However, in order to achieve this result, the query solution needs to be
changed, because the current query only lists the items that have bids. So I
rewrite the query as follow:
<result>
   FOR $seller  IN document("users.xml")//user_tuple,  $item    IN
document("items.xml")//item_tuple
   LET $highbid := max(document("bids.xml")//bid_tuple[itemno =
$item/itemno]/bid),
         $bidderId := document("bids.xml")//bid_tuple[bid =
$highbid]/userid,
         $buyername := document("users.xml")//user_tuple[userid =
$bidderId]/name
   WHERE $seller/name = "Tom Jones"
     AND $seller/userid = $item/offered_by
     AND contains($item/description, "Bicycle")
   RETURN
      <jones_bike>
         $item/itemno ,
         $item/description ,
         <high_bid> $highbid</high_bid> ,
         <high_bidder> $buyername </high_bidder>
      </jones_bike> SORTBY (itemno)
</result>
I run this query using my own XQuery engine (I'm implementing it for my
master degree project), and it gives the expected result.
Let me know your thoughts on this.

Thanks,
Fangqi Hu