I'm currently learning how to work with xml documents. I've got as far as finding out about XML::Simple and working though some examples. Here is my 'test script' as it is at the moment. 
#!/usr/bin/perl

# use module
use XML::Simple;
use Data::Dumper;

$xs = new XML::Simple(keeproot => 1,searchpath => ".",
      forcearray => 1,);

$ref = $xs->XMLin("test.xml");

print Dumper($ref);

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And my data dump looks like this. 
$VAR1 = {
          'sas_residue_annotation' => [
                                        {
                                          'xmlns' => 'http://www.ebi.a
+c.uk/WSsas/Schema',
                                          'sources' => [
                                                       {
                                                         'source' => [
                                                                     {
                                                                      
+ 'source_name' => [
                                                                      
+                  '1iho'
                                                                      
+                ],
                                                                      
+ 'ref_evalue' => [
                                                                      
+                 '5.5e-50'
                                                                      
+               ],
                                                                      
+ 'ref_overlap' => [
                                                                      
+                  '282'
                                                                      
+                ],
                                                                      
+ 'ref_identity' => [
                                                                      
+                   '47.20'
                                                                      
+                 ],
                                                                      
+ 'ref_pmid' => [
                                                                      
+               '11377204'
                                                                      
+             ]
                                                                     }
+,
                                                                     {
                                                                      
+ 'source_name' => [
                                                                      
+                  '1mop'
                                                                      
+                ],
                                                                      
+ 'ref_evalue' => [
                                                                      
+                 '8.3e-38'
                                                                      
+               ],
                                                                      
+ 'ref_overlap' => [
                                                                      
+                  '264'
                                                                      
+                ],
                                                                      
+ 'ref_identity' => [
                                                                      
+                   '43.60'
                                                                      
+                 ],
                                                                      
+ 'ref_pmid' => [
                                                                      
+               '12717031'
                                                                      
+             ]
                                                                     }
+,
                                                                     {
                                                                      
+ 'source_name' => [
                                                                      
+                  '1n2b'
                                                                      
+                ],
                                                                      
+ 'ref_evalue' => [
                                                                      
+                 '8.2e-38'
                                                                      
+               ],
                                                                      
+ 'ref_overlap' => [
                                                                      
+                  '264'
                                                                      
+                ],
                                                                      
+ 'ref_identity' => [
                                                                      
+                   '43.60'
                                                                      
+                 ],
                                                                      
+ 'ref_pmid' => [
                                                                      
+               '12717031'
                                                                      
+             ]
                                                                     }
+,
etc ...

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I'm not sure how to go about retrieving the information - how I might, for example, just want to print off all the 'source names' in my file. I've tried following a few examples on this today and haven't been able to figure it out yet. Any tips much appreciated.

In reply to request for help on working with XML::Simple by Angharad

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