17.7 (a)


<keyref name="MustBeValidClass" refer="adm:CourseKey">
    <selector xpath="Students/Student/CrsTaken"/>
    <field xpath="@CrsCode"/>
</keyref>  

Here, adm is the namespace prefix used for the schema of the document 
in Fig 17.4 and CourseKey is defined as the primary key for Course 
elements:

<key name="CourseKey">
    <selector xpath="Courses/Course"/>
    <field xpath="@CrsCode"/>
</key>  


17.12 (a)

//Student[../CrsTaken/@CrsCode="MAT123" and ends-with(@StudId,"987")]

(b)

//Student[count(../CrsTaken) &lt 3  and starts-with(@Name,"Joe")]

17.14

<?xml version="1.0">
<xml:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xsl:version="1.0">

<xsl:template match="/">
   <StudentList1996>
      <xsl:apply-templates/>
   </StudentList1996>
</xsl:template>

<xsl:template match="//Student">
   <xsl:if test="../CrsTaken/@Semester='S1998'">
      <xsl:copy-of select="."/>
   </xsl:if>      
</xsl:template>

</xml:stylesheet>

17.21

(a) 

<StudentList> 
(
  FOR $s IN document("http://xyz.edu/student.xml")//tuple
  WHERE contains($s/Address/@value,"Main St")
  RETURN $s
)
</StudentList> 


(b) 

<CrsList>
(
  FOR $c IN document("http://xyz.edu/course.xml")//tuple
  WHERE NOT contains($c/CrsCode/@value,$c/DeptId/@value)
  RETURN $c
)
</CrsList>

(c)

<Teaching>
(
  FOR $tIN document("http://xyz.edu/teaching.xml")//tuple
  WHERE starts-with($t/Semester/@value,"F")
  RETURN $t
)
</Teaching>