As mentioned by Edan, I think XML::Twig is an excellent option for this kind of thing.

Below i have given some code which may u can modify for ur needs.

The below code will create three files named as per dc:identifier element.

For Further details see XML::Twig.

use XML::Twig;
undef $/; 
$x=<DATA>;
## i have assumed that dc:identifier as first child of rdf:Description
+.
$p=new XML::Twig(twig_roots=>{
    'rdf:Description'=>\&rdf},
    pretty_print => 'indented');
$p->parse($x);
sub rdf
{
    my ($a,$b)=@_;
    my $filename=$b->first_child_text;    
    open(FOUT,">$filename") or die("$filename not opened for writing\n
+");
    print FOUT q(<?xml version="1.0" encoding="UTF-8"?>); 
    print FOUT $b->sprint;
    close(FOUT);
}
__DATA__
<?xml version="1.0" encoding="UTF-8"?>
<ab:root>
<rdf:Description>
<dc:identifier>ab.xml</dc:identifier>
<dc:abc>abc</dc:abc>
</rdf:Description>
<rdf:Description>
<dc:identifier>bc.xml</dc:identifier>
<dc:abc>bcd</dc:abc>
</rdf:Description>
<rdf:Description>
<dc:identifier>ef.xml</dc:identifier>
<dc:abc>efg</dc:abc>
</rdf:Description>
</ab:root>
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