(:
XML Query Use Cases: http://www.w3.org/TR/xquery-use-cases/
Copyright ©2003 World Wide Web Consortium, (Massachusetts Institute of Technology, European Research Consortium for Informatics and Mathematics, Keio University). All Rights Reserved. This work is distributed under the W3C® Software License [1] in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
[1] http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231
 Filename: rQ3.xq :)

(: Section: 1.4.4.3 Q3  Find cases where a user with a rating worse 
(alphabetically, greater)  than "C" is offering an item with a reserve 
price of more than 1000. :)

<result>
  {
    for $u in doc("users.xml")//user_tuple
    for $i in doc("items.xml")//item_tuple
    where $u/rating > "C" 
       and $i/reserve_price > 1000 
       and $i/offered_by = $u/userid
    return
        <warning>
            { $u/name }
            { $u/rating }
            { $i/description }
            { $i/reserve_price }
        </warning>
  }
</result>