• The CDs themselves have an artist and title fields.
• So it should be possible to search for CDs of a particular artist
• The key is the contents of the artist field
• In this case the key may return a set of artist nodes
• Use xsl:for-each to go through these finding the contents of the associated title element

            <xsl:key name="lookupartist" match="cd/artist" use="." />
<xsl:key name="pricekey" match="price" use="@ticket" />

<xsl:template match="/cdlist">
 <h3>CDs by Louis Armstrong</h3>

 <xsl:for-each select="key('lookupartist','Armstrong, Louis')" >
  <pre><text>Title: </text><xsl:value-of select="../title" />
   <xsl:variable name="pricecolor" select="../@price" />
   <text> ,Price: </text><xsl:value-of select="key('pricekey' , $pricecolor)" />
  </pre>
 </xsl:for-each>
</xsl:template>

Result