XML Query Use Cases

<!ELEMENT bib  (book* )>
<!ELEMENT book  (title,  (author+ | editor+ ), publisher, price )>
<!ATTLIST book  year CDATA  #REQUIRED >
<!ELEMENT author  (last, first )>
<!ELEMENT editor  (last, first, affiliation )>
<!ELEMENT title  (#PCDATA )>
<!ELEMENT last  (#PCDATA )>
<!ELEMENT first  (#PCDATA )>
<!ELEMENT affiliation  (#PCDATA )>
<!ELEMENT publisher  (#PCDATA )>
<!ELEMENT price  (#PCDATA )>

<bib>
    <book year="1994">
       <title>TCP/IP Illustrated</title>
        <author><last>Stevens</last><first>W.</first></author>
        <publisher>Addison-Wesley</publisher>
        <price> 65.95</price>
   </book>
   <book year="1992">
        <title>Advanced Programming in the Unix environment</title>
        <author><last>Stevens</last><first>W.</first></author>
        <publisher>Addison-Wesley</publisher>
        <price>65.95</price>
   </book>
   <book year="2000">
       <title>Data on the Web</title>
        <author><last>Abiteboul</last><first>Serge</first></author>
        <author><last>Buneman</last><first>Peter</first></author>
        <author><last>Suciu</last><first>Dan</first></author>
        <publisher>Morgan Kaufmann Publishers</publisher>
       <price>39.95</price>
   </book>
   <book year="1999">
        <title>The Economics of Technology and Content for Digital TV</title>
       <editor>
               <last>Gerbarg</last><first>Darcy</first>
                <affiliation>CITI</affiliation>
       </editor>
            <publisher>Kluwer Academic Publishers</publisher>
       <price>129.95</price>
   </book>
</bib>

<!ELEMENT reviews (entry*)>
<!ELEMENT entry  (title, price, review)>
<!ELEMENT title  (#PCDATA)>
<!ELEMENT price  (#PCDATA)>
<!ELEMENT review (#PCDATA)>

<reviews>
   <entry>
        <title>Data on the Web</title>
        <price>34.95</price>
        <review>
               A very good discussion of semi-structured database
               systems and XML.
        </review>
    </entry>
    <entry>
        <title>Advanced Programming in the Unix environment</title>
        <price>65.95</price>
        <review>
               A clear and detailed discussion of UNIX programming.
        </review>
    </entry>
    <entry>
        <title>TCP/IP Illustrated</title>
        <price>65.95</price>
        <review>
               One of the best books on TCP/IP.
        </review>
    </entry>
</reviews>

<!ELEMENT chapter (title, section*)>
<!ELEMENT section (title, section*)>
<!ELEMENT title (#PCDATA)>

<chapter>
    <title>Data Model</title>
    <section>
        <title>Syntax For Data Model</title>
    </section>
    <section>
        <title>XML</title>
        <section>
            <title>Basic Syntax</title>
        </section>
        <section>
            <title>XML and Semistructured Data</title>
        </section>
    </section>
</chapter>

<!ELEMENT prices (book*)>
<!ELEMENT book (title, source, price)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT source (#PCDATA)>
<!ELEMENT price (#PCDATA)>

<prices>
    <book>
        <title>Advanced Programming in the Unix environment</title>
        <source>www.amazon.com</source>
        <price>65.95</price>
    </book>
    <book>
        <title>Advanced Programming in the Unix environment</title>
        <source>www.bn.com</source>
        <price>65.95</price>
    </book>
    <book>
        <title>TCP/IP Illustrated</title>
        <source>www.amazon.com</source>
        <price>65.95</price>
    </book>
    <book>
        <title>TCP/IP Illustrated</title>
        <source>www.bn.com</source>
        <price>65.95</price>
    </book>
    <book>
        <title>Data on the Web</title>
        <source>www.amazon.com</source>
        <price>34.95</price>
    </book>
    <book>
        <title>Data on the Web</title>
        <source>www.bn.com</source>
        <price>39.95</price>
    </book>
</prices>

<bib>
 {
  for $b in document("http://www.bn.com/bib.xml")/bib/book
  where $b/publisher = "Addison-Wesley" and $b/@year > 1991
  return
    <book year="{ $b/@year }">
     { $b/title }
    </book>
 }
</bib>

<bib>
    <book year="1994">
        <title>TCP/IP Illustrated</title>
    </book>
    <book year="1992">
        <title>Advanced Programming in the Unix environment</title>
    </book>
</bib>

<results>
  {
    for $b in document("http://www.bn.com/bib.xml")/bib/book,
        $t in $b/title,
        $a in $b/author
    return
        <result>
            { $t }   
            { $a }
        </result>
  }
</results>

<results>
    <result>
        <title>TCP/IP Illustrated</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </result>
    <result>
        <title>Advanced Programming in the Unix environment</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </result>
    <result>
        <title>Data on the Web</title>
        <author>
            <last>Abiteboul</last>
            <first>Serge</first>
        </author>
    </result>
    <result>
        <title>Data on the Web</title>
        <author>
            <last>Buneman</last>
            <first>Peter</first>
        </author>
    </result>
    <result>
        <title>Data on the Web</title>
        <author>
            <last>Suciu</last>
            <first>Dan</first>
        </author>
    </result>
</results>

<results>
{
    for $b in document("http://www.bn.com/bib.xml")/bib/book
    return
        <result>
            { $b/title }
            { $b/author  }
        </result>
}
</results>

<results>
    <result>
        <title>TCP/IP Illustrated</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </result>
    <result>
        <title>Advanced Programming in the Unix environment</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </result>
    <result>
        <title>Data on the Web</title>
        <author>
            <last>Abiteboul</last>
            <first>Serge</first>
        </author>
        <author>
            <last>Buneman</last>
            <first>Peter</first>
        </author>
        <author>
            <last>Suciu</last>
            <first>Dan</first>
        </author>
    </result>
    <result>
        <title>The Economics of Technology and Content for Digital TV</title>
    </result>
</results>

<results>
  {
    for $a in distinct-values(document("http://www.bn.com/bib.xml")//author)
    return
        <result>
            { $a }
            {
                for $b in document("http://www.bn.com/bib.xml")/bib/book
                where some $ba in $b/author satisfies deep-equal($ba,$a)
                return $b/title
            }
        </result>
  }
</results>

<results>
    <result>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
        <title>TCP/IP Illustrated</title>
        <title>Advanced Programming in the Unix environment</title>
    </result>
    <result>
        <author>
            <last>Abiteboul</last>
            <first>Serge</first>
        </author>
        <title>Data on the Web</title>
    </result>
    <result>
        <author>
            <last>Buneman</last>
            <first>Peter</first>
        </author>
        <title>Data on the Web</title>
    </result>
    <result>
        <author>
            <last>Suciu</last>
            <first>Dan</first>
        </author>
        <title>Data on the Web</title>
    </result>
</results>

<books-with-prices>
  {
    for $b in document("http://www.bn.com/bib.xml")//book,
        $a in document("http://www.amazon.com/reviews.xml")//entry
    where $b/title = $a/title
    return
        <book-with-prices>
            { $b/title }
            <price-amazon>{ $a/price/text() }</price-amazon>
            <price-bn>{ $b/price/text() }</price-bn>
        </book-with-prices>
  }
</books-with-prices>

<books-with-prices>
    <book-with-prices>
        <title>TCP/IP Illustrated</title>
        <price-amazon>65.95</price-amazon>
        <price-bn> 65.95</price-bn>
    </book-with-prices>
    <book-with-prices>
        <title>Advanced Programming in the Unix environment</title>
        <price-amazon>65.95</price-amazon>
        <price-bn>65.95</price-bn>
    </book-with-prices>
    <book-with-prices>
        <title>Data on the Web</title>
        <price-amazon>34.95</price-amazon>
        <price-bn>39.95</price-bn>
    </book-with-prices>
</books-with-prices>

<bib>
  {
    for $b in document("http://www.bn.com/bib.xml")//book
    where count($b/author) > 0
    return
        <book>
            { $b/title }
            {
                for $a in $b/author[position()<=2] 
                return $a
            }
            {
                if (count($b/author) > 2)
                then <et-al/>
                else ()
            }
        </book>
  }
</bib>

<bib>
    <book>
        <title>TCP/IP Illustrated</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </book>
    <book>
        <title>Advanced Programming in the Unix environment</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </book>
    <book>
        <title>Data on the Web</title>
        <author>
            <last>Abiteboul</last>
            <first>Serge</first>
        </author>
        <author>
            <last>Buneman</last>
            <first>Peter</first>
        </author>
        <et-al/>
    </book>
</bib>

<bib>
  {
    for $b in document("http://www.bn.com/bib.xml")//book
    where $b/publisher = "Addison-Wesley" and $b/@year > 1991
    return
        <book>
            { $b/@year }
            { $b/title }
        </book>
    sort by (title)
  }
</bib>

<bib>
    <book year="1992">
        <title>Advanced Programming in the Unix environment</title>
    </book>
    <book year="1994">
        <title>TCP/IP Illustrated</title>
    </book>
</bib>    

for $b in document("http://www.bn.com/bib.xml")//book
let $e := $b/*[contains(string(.), "Suciu")
               and ends-with(local-name(.), "or")]
where exists($e)
return
    <book>
        { $b/title }
        { $e }
    </book>

<book>
        <title>Data on the Web</title>
        <author>
            <last>Suciu</last>
            <first>Dan</first>
        </author>
 </book>

<results>
  {
    for $t in document("books.xml")//(chapter | section)/title
    where contains($t/text(), "XML")
    return $t
  }
</results>

<results>
    <title>XML</title>
    <title>XML and Semistructured Data</title>
</results>

<results>
  {
    let $doc := document("prices.xml")
    for $t in distinct-values($doc//book/title)
    let $p := for $x in $doc//book[title = $t]/price
              return decimal($x)
    return
      <minprice title="{ $t/text() }">
        <price>{ min($p) }</price>
      </minprice>
  }
</results>

<results>
    <minprice title="Advanced Programming in the Unix environment">
        <price>65.95</price>
    </minprice>
    <minprice title="TCP/IP Illustrated">
        <price>65.95</price>
    </minprice>
    <minprice title="Data on the Web">
        <price>34.95</price>
    </minprice>
</results>

<bib>
{
        for $b in document("http://www.bn.com/bib.xml")//book[author]
        return
            <book>
                { $b/title }
                { $b/author }
            </book>
}
{
        for $b in document("http://www.bn.com/bib.xml")//book[editor]
        return
          <reference>
            { $b/title }
            {$b/editor/affiliation}
          </reference>
}
</bib> 

<bib>
    <book>
        <title>TCP/IP Illustrated</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </book>
    <book>
        <title>Advanced Programming in the Unix environment</title>
        <author>
            <last>Stevens</last>
            <first>W.</first>
        </author>
    </book>
    <book>
        <title>Data on the Web</title>
        <author>
            <last>Abiteboul</last>
            <first>Serge</first>
        </author>
        <author>
            <last>Buneman</last>
            <first>Peter</first>
        </author>
        <author>
            <last>Suciu</last>
            <first>Dan</first>
        </author>
    </book>
    <reference>
        <title>The Economics of Technology and Content for Digital TV</title>
        <affiliation>CITI</affiliation>
    </reference>
</bib>

<bib>
{
    for $book1 in document("http://www.bn.com/bib.xml")//book,
        $book2 in document("http://www.bn.com/bib.xml")//book
    let $aut1 := for $a in $book1/author
order by $a/last, $a/first
return $a
    let $aut2 := for $a in $book2/author
order by $a/last, $a/first
return $a
    where $book1 << $book2
    and not($book1/title = $book2/title)
    and sequence-deep-equal($aut1, $aut2)
    return
        <book-pair>
            { $book1/title }
            { $book2/title }
        </book-pair>
}
</bib>

<bib>
    <book-pair>
        <title>TCP/IP Illustrated</title>
        <title>Advanced Programming in the Unix environment</title>
    </book-pair>
</bib>

<!DOCTYPE book [
  <!ELEMENT book (title, author+, section+)>
  <!ELEMENT title (#PCDATA)>
  <!ELEMENT author (#PCDATA)>
  <!ELEMENT section (title, (p | figure | section)* )>
  <!ATTLIST section
      id         ID    #IMPLIED
      difficulty CDATA #IMPLIED>
  <!ELEMENT p (#PCDATA)>
  <!ELEMENT figure (title, image)>
  <!ATTLIST figure
       width   CDATA   #REQUIRED
       height  CDATA   #REQUIRED >
  <!ELEMENT image EMPTY>
  <!ATTLIST image
       source  CDATA   #REQUIRED >
]>

<?xml version="1.0"?>
<!DOCTYPE book SYSTEM "book.dtd">
<book>
  <title>Data on the Web</title>
  <author>Serge Abiteboul</author>
  <author>Peter Buneman</author>
  <author>Dan Suciu</author>
  <section id="intro" difficulty="easy" >
    <title>Introduction</title>
    <p>Text ... </p>
    <section>
      <title>Audience</title>
      <p>Text ... </p>
    </section>
    <section>
      <title>Web Data and the Two Cultures</title>
      <p>Text ... </p>
      <figure height="400" width="400">
        <title>Traditional client/server architecture</title>
        <image source="csarch.gif"/>
      </figure>
      <p>Text ... </p>
    </section>
  </section>
  <section id="syntax" difficulty="medium" >
    <title>A Syntax For Data</title>
    <p>Text ... </p>
    <figure height="200" width="500">
      <title>Graph representations of structures</title>
      <image source="graphs.gif"/>
    </figure>
    <p>Text ... </p>
    <section>
      <title>Base Types</title>
      <p>Text ... </p>
    </section>
    <section>
      <title>Representing Relational Databases</title>
      <p>Text ... </p>
      <figure height="250" width="400">
        <title>Examples of Relations</title>
        <image source="relations.gif"/>
      </figure>
    </section>
    <section>
      <title>Representing Object Databases</title>
      <p>Text ... </p>
    </section>      
  </section>
</book>

define function toc( element $e )
  returns element*
{
  let $n := local-name( $e )
  return
    if ($n = "section")
    then
        <section>
           { $e/@* }
           { toc($e/*) }
        </section>
    else if ($n = "title")
    then $e
    else ()
}
<toc>
  {
    toc( document("book1.xml")/book )
  }
</toc>

<toc>
    <section id="intro" difficulty="easy">
        <title>Introduction</title>
        <section>
            <title>Audience</title>
        </section>
        <section>
            <title>Web Data and the Two Cultures</title>
        </section>
    </section>
    <section id="syntax" difficulty="medium">
        <title>A Syntax For Data</title>
        <section>
            <title>Base Types</title>
        </section>
        <section>
            <title>Representing Relational Databases</title>
        </section>
        <section>
            <title>Representing Object Databases</title>
        </section>
    </section>
</toc>

<figlist>
  {
    for $f in document("book1.xml")//figure
    return
        <figure>
            { $f/@* }
            { $f/title }
        </figure>
  }
</figlist>

<figlist>
    <figure  height="400" width="400">
        <title>Traditional client/server architecture</title>
    </figure>
    <figure  height="200" width="500">
        <title>Graph representations of structures</title>
    </figure>
    <figure  height="250" width ="400">
        <title>Examples of Relations</title>
    </figure>
</figlist>

<section_count>{ count(document("book.xml")//section) }</section_count>,
<figure_count>{ count(document("book.xml")//figure) }</figure_count>

<section_count>7</section_count>
<figure_count>3</figure_count>

<top_section_count>
 {
   count(document("book.xml")/book/section)
 }
</top_section_count>

<top_section_count>2</top_section_count>

<section_list>
  {
    for $s in document("book.xml")//section
    let $f := $s/figure
    return
        <section title="{ $s/title/text() }" figcount="{ count($f) }"/>
  }
</section_list>

<section_list>
    <section title="Introduction" figcount="0"/>
    <section title="Audience" figcount="0"/>
    <section title="Web Data and the Two Cultures" figcount="1"/>
    <section title="A Syntax For Data" figcount="1"/>
    <section title="Base Types" figcount="0"/>
    <section title="Representing Relational Databases" figcount="1"/>
    <section title="Representing Object Databases" figcount="0"/>
</section_list>

define function section_summary($s as element) as element
{
    <section>
        { $s/@* }
        { $s/title }
        <figcount>{ count($s/figure) }</figcount>
        {
            for $ss in $s/section
            return section_summary($ss)
        }
    </section>
}
<toc>
  {
    for $s in document("book.xml")/book/section
    return section_summary($s)
  }
</toc>

<toc>
    <section id="intro" difficulty="easy">
        <title>Introduction</title>
        <figcount>0</figcount>
        <section>
            <title>Audience</title>
            <figcount>0</figcount>
        </section>
        <section>
            <title>Web Data and the Two Cultures</title>
            <figcount>1</figcount>
        </section>
    </section>
    <section id="syntax" difficulty="medium">
        <title>A Syntax For Data</title>
        <figcount>1</figcount>
        <section>
            <title>Base Types</title>
            <figcount>0</figcount>
        </section>
        <section>
            <title>Representing Relational Databases</title>
            <figcount>1</figcount>
        </section>
        <section>
            <title>Representing Object Databases</title>
            <figcount>0</figcount>
        </section>
    </section>
</toc>

<!DOCTYPE report [
  <!ELEMENT report (section*)>
  <!ELEMENT section (section.title, section.content)>
  <!ELEMENT section.title  (#PCDATA )>
  <!ELEMENT section.content  (#PCDATA | anesthesia | prep
                            | incision | action | observation )*>
  <!ELEMENT anesthesia (#PCDATA)>
  <!ELEMENT prep ( (#PCDATA | action)* )>
  <!ELEMENT incision ( (#PCDATA | geography | instrument)* )>
  <!ELEMENT action ( (#PCDATA | instrument )* )>
  <!ELEMENT observation (#PCDATA)>
  <!ELEMENT geography (#PCDATA)>
  <!ELEMENT instrument (#PCDATA)>
]>

<report>
  <section>
    <section.title>Procedure</section.title>
     <section.content>
      The patient was taken to the operating room where she was placed
      in supine position and
      <anesthesia>induced under general anesthesia.</anesthesia>
      <prep>
        <action>A Foley catheter was placed to decompress the bladder</action>
        and the abdomen was then prepped and draped in sterile fashion.
      </prep> 
      <incision>
        A curvilinear incision was made
        <geography>in the midline immediately infraumbilical</geography>
        and the subcutaneous tissue was divided
        <instrument>using electrocautery.</instrument>
      </incision>
      The fascia was identified and
      <action>#2 0 Maxon stay sutures were placed on each side of the midline.
      </action>
      <incision>
        The fascia was divided using
        <instrument>electrocautery</instrument>
        and the peritoneum was entered.
      </incision>
      <observation>The small bowel was identified.</observation>
      and
      <action>
        the
        <instrument>Hasson trocar</instrument>
        was placed under direct visualization.
      </action>
      <action>
        The
        <instrument>trocar</instrument>
        was secured to the fascia using the stay sutures.
      </action>
     </section.content>
  </section>
</report>

for $s in document("report1.xml")//section[section.title = "Procedure"]
return ($s//incision)[2]/instrument

<instrument>electrocautery</instrument>

for $s in document("report1.xml")//section[section.title = "Procedure"]
return ($s//instrument)[position()<=2]

<instrument>using electrocautery.</instrument>
<instrument>electrocautery</instrument>

let $i2 := (document("report1.xml")//incision)[2]
for $a in (document("report1.xml")//action)[. >> $i2][position()<=2]
return $a//instrument

<instrument>Hasson trocar</instrument>
<instrument>trocar</instrument>

for $p in document("report1.xml")//section[section.title = "Procedure"]
where not(some $a in $p//anesthesia satisfies
        $a << ($p//incision)[1] )
return $p

define function precedes($a as node, $b as node) as boolean
{
    $a << $b
      and
    empty($a//node() intersect $b)
}
define function follows($a as node, $b as node) as boolean
{
    $a >> $b
      and
    empty($b//node() intersect $a)
}
<critical_sequence>
 {
  let $proc := document("report1.xml")//section[section.title="Procedure"][1]
  for $n in $proc//node()
  where follows($n, ($proc//incision)[1])
    and precedes($n, ($proc//incision)[2])
  return $n
 }
</critical_sequence>

<critical_sequence>
 {
  let $proc := document("report1.xml")//section[section.title="Procedure"][1],
      $i1 :=  ($proc//incision)[1],
      $i2 :=  ($proc//incision)[2]
  for $n in $proc//node() except $i1//node()
  where $n >> $i1 and $n << $i2
  return $n
 }
</critical_sequence>

<critical_sequence>
      The fascia was identified and
      <action>#2 0 Maxon stay sutures were placed on each side of the midline.</action>#2 0 Maxon stay sutures were placed on each side of the midline.
</critical_sequence>

USERS ( USERID, NAME, RATING )
ITEMS ( ITEMNO, DESCRIPTION, OFFERED_BY, START_DATE, END_DATE, RESERVE_PRICE )
BIDS ( USERID, ITEMNO, BID, BID_DATE )

<!DOCTYPE users [
  <!ELEMENT users   (user_tuple*)>
  <!ELEMENT user_tuple (userid, name, rating?)>
  <!ELEMENT userid  (#PCDATA)>
  <!ELEMENT name    (#PCDATA)>
  <!ELEMENT rating  (#PCDATA)>
]>
<!DOCTYPE items [
  <!ELEMENT items       (item_tuple*)>
  <!ELEMENT item_tuple  (itemno, description, offered_by,
                              start_date?, end_date?, reserve_price? )>
  <!ELEMENT itemno      (#PCDATA)>
  <!ELEMENT description (#PCDATA)>
  <!ELEMENT offered_by  (#PCDATA)>
  <!ELEMENT start_date  (#PCDATA)>
  <!ELEMENT end_date    (#PCDATA)>
  <!ELEMENT reserve_price (#PCDATA)>
]>
<!DOCTYPE bids [
  <!ELEMENT bids      (bid_tuple*)>
  <!ELEMENT bid_tuple (userid, itemno, bid, bid_date)>
  <!ELEMENT userid    (#PCDATA)>
  <!ELEMENT itemno    (#PCDATA)>
  <!ELEMENT bid       (#PCDATA)>
  <!ELEMENT bid_date  (#PCDATA)>
]>

<items>
  <item_tuple>
    <itemno>1001</itemno>
    <description>Red Bicycle</description>
    <offered_by>U01</offered_by>
    <start_date>1999-01-05</start_date>
    <end_date>1999-01-20</end_date>
    <reserve_price>40</reserve_price>
  </item_tuple>
  <!-- !!! Snip !!! -->
<users>
  <user_tuple>
    <userid>U01</userid>
    <name>Tom Jones</name>
    <rating>B</rating>
  </user_tuple>
  <!-- !!! Snip !!! -->
<bids>
  <bid_tuple>
    <userid>U02</userid>
    <itemno>1001</itemno>
    <bid>35</bid>
    <bid_date>1999-01-07</bid_date>
    </bid_tuple>
  <bid_tuple>
  <!-- !!! Snip !!! -->

<result>
  {
    for $i in document("items.xml")//item_tuple
    where $i/start_date <= current-date()
      and $i/end_date >= current-date()
      and contains($i/description, "Bicycle")
    order by $1/itemno
return
        <item_tuple>
            { $i/itemno }
            { $i/description }
        </item_tuple>
  }
</result>

<result>
    <item_tuple>
        <itemno>1003</itemno>
        <description>Old Bicycle</description>
    </item_tuple>
    <item_tuple>
        <itemno>1007</itemno>
        <description>Racing Bicycle</description>
    </item_tuple>
</result>

<result>
  {
    for $i in document("items.xml")//item_tuple
    let $b := document("bids.xml")//bid_tuple[itemno = $i/itemno]
    where contains($i/description, "Bicycle")
    order by $1/itemno
return
        <item_tuple>
            { $i/itemno }
            { $i/description }
            <high_bid>{ max(for $z in $b/bid return decimal($z)) }</high_bid>
        </item_tuple>
  }
</result>

<result>
<item_tuple>
<itemno>1001</itemno>
            <description>Red Bicycle</description>
            <high_bid>55.0</high_bid>
</item_tuple><item_tuple>
<itemno>1003</itemno>
            <description>Old Bicycle</description>
            <high_bid>20.0</high_bid>
</item_tuple><item_tuple>
<itemno>1007</itemno>
            <description>Racing Bicycle</description>
            <high_bid>225.0</high_bid>
</item_tuple><item_tuple>
<itemno>1008</itemno>
            <description>Broken Bicycle</description>
            <high_bid></high_bid>
</item_tuple>
</result>

<result>
  {
    for $u in document("users.xml")//user_tuple
    for $i in document("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>

<result>
    <warning>
        <name>Dee Linquent</name>
        <rating>D</rating>
        <description>Helicopter</description>
        <reserve_price>50000</reserve_price>
    </warning>
</result>

<result>
  {
    for $i in document("items.xml")//item_tuple
    where empty(document("bids.xml")//bid_tuple[itemno = $i/itemno])
    return
        <no_bid_item>
            { $i/itemno }
            { $i/description }
        </no_bid_item>
  }
</result>

<result>
    <no_bid_item>
&