I'm updating this post to show you working code for that piece o xml.
On the XML I had to add the nodes <NCI_PID_XML> and <Ontology> 
<NCI_PID_XML>
  <Ontology>
    <LabelType name="function" id="8">
      <LabelValueList>
        <LabelValue name="acyltransferase activity" id="8007" parent_i
+dref="8000" GO="GO:0008415" />
        <LabelValue name="calcium- and calmodulin-responsive adenylate
+ cyclase activity" id="8008" parent_idref="8000" GO="GO:0008294" /
>
        <LabelValue name="casein kinase I activity" id="11900" parent_
+idref="8000" GO="GO:0004681" />
        <LabelValue name="casein kinase activity" id="9634" parent_idr
+ef="8000" GO="GO:0004680" />
        <LabelValue name="function" id="75" parent_idref="75" />
        <LabelValue name="guanylate cyclase activity" id="8009" parent
+_idref="8000" GO="GO:0004383" />
        <LabelValue name="interleukin-12 receptor activity" id="8015" 
+parent_idref="8000" GO="GO:0016517" />
        <LabelValue name="metalloendopeptidase activity" id="8010" par
+ent_idref="8000" GO="GO:0004222" />
        <LabelValue name="molecular_function" id="8000" parent_idref="
+75" GO="GO:0003674" />
        <LabelValue name="potassium channel inhibitor activity" id="10
+264" parent_idref="8000" GO="GO:0019870" />
        <LabelValue name="protein serine/threonine phosphatase activit
+y" id="8002" parent_idref="8000" GO="GO:0004722" />
        <LabelValue name="protein tyrosine phosphatase activity" id="8
+013" parent_idref="8000" GO="GO:0004725" />
        <LabelValue name="retinol isomerase activity" id="8012" parent
+_idref="8000" GO="GO:0050251" />
        <LabelValue name="serine protease" id="8003" parent_idref="800
+0" />
        <LabelValue name="specific transcriptional repressor activity"
+ id="8019" parent_idref="8000" GO="GO:0016566" />
        <LabelValue name="telomeric DNA binding" id="8005" parent_idre
+f="8000" GO="GO:0042162" />
        <LabelValue name="transcription factor activity" id="8018" par
+ent_idref="8000" GO="GO:0003700" />
        <LabelValue name="transcription repressor activity" id="8017" 
+parent_idref="8000" GO="GO:0016564" />
        <LabelValue name="tumor necrosis factor receptor activity" id=
+"8004" parent_idref="8000" GO="GO:0005031" />
      </LabelValueList>
    </LabelType>
  </Ontology>
</NCI_PID_XML>

[download]
Also changed your code to cycle through the LabelValue nodes and call getAttribute on them.
Also closed the file at the end and corrected typos for $id and $name. 
#!/usr/bin/perl 
use strict;
use XML::XPath;
my $file = "nci.xml";
my $xp = XML::XPath-> new(filename => $file);
open(info,"+>nci.txt");
foreach my $concept ($xp->findnodes('/NCI_PID_XML/Ontology/LabelType')
+) {

    my $parentid = $concept->getAttribute('id');
    my $type = $concept->getAttribute('name');
    foreach my $LabelValue ( $concept->findnodes('LabelValueList/Label
+Value')) {
        my $id =  $LabelValue->getAttribute('id');
        my $name =  $LabelValue->getAttribute('name');
        my $goid =  $LabelValue->getAttribute('GO');

        print info "$parentid\t";
        print info "$type\t";
        print info "$id\t";
        print info "$name\t";
        print info "$goid\n";
    }
}
close info;

[download]
And on the nci.txt file I now have 
8       function        8007    acyltransferase activity        GO:000
+8415
8       function        8008    calcium- and calmodulin-responsive ade
+nylate cyclase activity   GO:0008294
8       function        11900   casein kinase I activity        GO:000
+4681
8       function        9634    casein kinase activity  GO:0004680
8       function        75      function
8       function        8009    guanylate cyclase activity      GO:000
+4383
8       function        8015    interleukin-12 receptor activity      
+  GO:0016517
8       function        8010    metalloendopeptidase activity   GO:000
+4222
8       function        8000    molecular_function      GO:0003674
8       function        10264   potassium channel inhibitor activity  
+  GO:0019870
8       function        8002    protein serine/threonine phosphatase a
+ctivity   GO:0004722
8       function        8013    protein tyrosine phosphatase activity 
+  GO:0004725
8       function        8012    retinol isomerase activity      GO:005
+0251
8       function        8003    serine protease
8       function        8019    specific transcriptional repressor act
+ivity     GO:0016566
8       function        8005    telomeric DNA binding   GO:0042162
8       function        8018    transcription factor activity   GO:000
+3700
8       function        8017    transcription repressor activity      
+  GO:0016564
8       function        8004    tumor necrosis factor receptor activit
+y GO:0005031

[download]

In reply to Re^3: problems with Xpath by olus
in thread problems with Xpath by Anonymous Monk

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