Extract attribute value if child node contains this text

Given this xml input:

<?xml version="1.0" encoding="UTF-8"?>
<atom:entry xmlns:atom="http://www.w3.org/2005/Atom" xmlns:dcterms="http://purl.org/dc/terms/" xmlns:doc="http://www.lyncode.com/xoai" xmlns:ore="http://www.openarchives.org/ore/terms/" xmlns:oreatom="http://www.openarchives.org/ore/atom/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3.org/2005/Atom http://www.kbcafe.com/rss/atom.xsd.xml">  
  <atom:id>http://hdl.handle.net/10862/152/ore.xml</atom:id>  
  <atom:link href="http://hdl.handle.net/10862/152" rel="alternate"/>  
  <atom:link href="http://hdl.handle.net/10862/152/ore.xml" rel="http://www.openarchives.org/ore/terms/describes"/>  
  <atom:link href="http://hdl.handle.net/10862/152/ore.xml#atom" rel="self" type="application/atom+xml"/>  
  <atom:published>2011-06-07T06:45:26Z</atom:published>  
  <atom:updated>2011-06-07T06:45:26Z</atom:updated>  
  <atom:source> 
    <atom:generator>SEAFDEC/AQD Institutional Repository</atom:generator> 
  </atom:source>  
  <atom:title>Field guide for the edible crustacea of the Philippines</atom:title>  
  <atom:author> 
    <atom:name>Motoh, Hiroshi</atom:name> 
  </atom:author>  
  <atom:category label="Aggregation" scheme="http://www.openarchives.org/ore/terms/" term="http://www.openarchives.org/ore/terms/Aggregation"/>  
  <atom:category scheme="http://www.openarchives.org/ore/atom/modified" term="2011-06-07T06:45:26Z"/>  
  <atom:category label="DSpace Item" scheme="http://www.dspace.org/objectModel/" term="DSpaceItem"/>  
  <atom:link href="https://repository.seafdec.org.ph/bitstream/10862/152/1/ediblecrustacea.pdf" length="2310365" rel="http://www.openarchives.org/ore/terms/aggregates" title="ediblecrustacea.pdf" type="application/pdf"/>  
  <atom:link href="https://repository.seafdec.org.ph/bitstream/10862/152/4/edible-crust-errata.pdf" length="177699" rel="http://www.openarchives.org/ore/terms/aggregates" title="edible-crust-errata.pdf" type="application/pdf"/>  
  <oreatom:triples> 
    <rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="http://hdl.handle.net/10862/152/ore.xml#atom">  
      <rdf:type rdf:resource="http://www.dspace.org/objectModel/DSpaceItem"/>  
      <dcterms:modified>2011-06-07T06:45:26Z</dcterms:modified> 
    </rdf:Description>  
    <rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="https://repository.seafdec.org.ph/bitstream/10862/152/35/edible-crust-errata.pdf.txt">  
      <rdf:type rdf:resource="http://www.dspace.org/objectModel/DSpaceBitstream"/>  
      <dcterms:description>TEXT</dcterms:description> 
    </rdf:Description>  
    <rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="https://repository.seafdec.org.ph/bitstream/10862/152/36/ediblecrustacea.pdf.txt">  
      <rdf:type rdf:resource="http://www.dspace.org/objectModel/DSpaceBitstream"/>  
      <dcterms:description>TEXT</dcterms:description> 
    </rdf:Description>  
    <rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="https://repository.seafdec.org.ph/bitstream/10862/152/1/ediblecrustacea.pdf">  
      <rdf:type rdf:resource="http://www.dspace.org/objectModel/DSpaceBitstream"/>  
      <dcterms:description>ORIGINAL</dcterms:description> 
    </rdf:Description>  
    <rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="https://repository.seafdec.org.ph/bitstream/10862/152/4/edible-crust-errata.pdf">  
      <rdf:type rdf:resource="http://www.dspace.org/objectModel/DSpaceBitstream"/>  
      <dcterms:description>ORIGINAL</dcterms:description> 
    </rdf:Description>  
    <rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="https://repository.seafdec.org.ph/bitstream/10862/152/32/ediblecrustacea.pdf.jpg">  
      <rdf:type rdf:resource="http://www.dspace.org/objectModel/DSpaceBitstream"/>  
      <dcterms:description>THUMBNAIL</dcterms:description> 
    </rdf:Description>  
    <rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="https://repository.seafdec.org.ph/bitstream/10862/152/33/edible-crust-errata.pdf.jpg">  
      <rdf:type rdf:resource="http://www.dspace.org/objectModel/DSpaceBitstream"/>  
      <dcterms:description>THUMBNAIL</dcterms:description> 
    </rdf:Description> 
      </oreatom:triples> 
    </atom:entry>

I would like to extract the value of the first occurence of rdf:Description[@rdf:about] if its child node contains the value of THUMBNAIL in the dcterms:description element. So in my example xml input above, I would like to extract https://repository.seafdec.org.ph/bitstream/10862/152/32/ediblecrustacea.pdf.jpg

EDIT:

This post is in relation to my previous post here: How to display thumbnails from harvested items in DSpace?

Basically, I want to achieve is to make the extracted value as a src for an image tag. So before clicking that downvote, please spare a moment to read that linked post.

Thanks in advance.

Solution

Maybe this will help you:

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dcterms="http://purl.org/dc/terms/">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/">
  <!-- You can use this XPath anywhere in the code.  -->
  <xsl:value-of select="//rdf:Description[boolean(@rdf:about) and 
                       .//dcterms:description[. = 'THUMBNAIL']][1]/@rdf:about"/>
</xsl:template>

</xsl:stylesheet>