Note 1: You can add element constructors, if you want to create
a new element to the output. For instance, in (2) below,
an original 'city' element is replaced by a new 'homecity'
element. The expression inside returns the text content of
the 'city' element. Compare this to $a/name which adds
an original 'name' element to the output.

Note 2: if the query is to be included in an XML document,
the '<' characters have to be replaced by character
entity references &lt;

------------------------------------------------------------------------

1

<adults>{
 for $a in document("studAddr.xml")/persons/person
 where $a/birthdate < 1983
 return $a/name
}</adults>


Result:

<adults>
<name>John Punin</name>
<name>John Smith</name>
<name>George Lucas</name>
</adults>


2

<students>{
 for $p in document("students.xml")/course/student,
     $a in document("studAddr.xml")/persons/person
 where $p/@id = $a/@id
 return 
	<student>{
	   $a/name
           <homecity>{$a/address/city/text()}</homecity>
           $p/project
	   }</student>
}</students>


Result:

<students>
  <student>
    <name>John Smith</name>
    <homecity>Buffalo</homecity>
    <project>80</project>
  </student>
  <student>
    <name>George Lucas</name>
    <homecity>Buffalo</homecity>
    <project>100</project>
  </student>
  <student>
    <name>Elizabeth Roberts</name>
    <homecity>Annapolis</homecity>
    <project>50</project>
  </student>
</students>

3

<students-by-city>{
 for $a in distinct-values(document("studAddr.xml")//city)
 return  $a
         for $b in document("studAddr.xml")/persons/person
	 for $c in document("students.xml")//student
         where value-equals($b/address/city,$a) and
	       $b/name = $c/name 
         return <student>{$b/name/text()}</student>
}</students-by-city>


Result:

<students-by-city>
<city>Annapolis</city>
<student>Elizabeth Roberts</student>
<city>Buffalo</city>
<student>John Smith</student>
<student>George Lucas</student>
</students-by-city>