sub GetMappletList
   {
        my $Target_node;
        my ($TableNm,$ColumnNm,$DomainNm,$AlgoNm);
        my @MaskingAlgorithmList;
        my @MappletNode;
       my $MpltRefFile_Dir = shift;
       my $MappletXmlName;
       open GET_MAPPLET_LIST, "<","$Profiler_Dir/$MpltRefFile_Dir/Inve
+ntory.rpt" or die "ERROR : Couldn't Open $Profiler_Dir/$MpltRefFile_D
+ir/Inventory.rpt $!";
       while (my $InvtoryCol = <GET_MAPPLET_LIST> )
              {         
                       chomp $InvtoryCol;
                       
                      ($TableNm,$ColumnNm,$DomainNm,$AlgoNm) = split(/
+,/,$InvtoryCol);
                      if ($TableNm =~ /$SourceTableName/)
                           {
                              print " The Workflow xml nme is $OutFile
+Name\n"; 
                              $MappletXmlName = "$Mapplet_Dir/$AlgoNm.
+XML";
                              print "The Dir name is $MappletXmlName\n
+";
                              my $MpltParser = XML::LibXML->new();
                              my $TargetXml = $MpltParser->parse_file(
+"$OutFileName");
                              my $MpltXml = $MpltParser->parse_file("$
+MappletXmlName");
                                my @MappletNode = $MpltXml->findnodes(
+'//MAPPLET');
                                my @TargetNode = $TargetXml->findnodes
+('//FOLDER');
                                #my $TargetRootNode = $TargetXml->find
+nodes('/POWERMART');
                                my $TargetRootNode   = $TargetXml->get
+DocumentElement;
                                                               
                              #$TargetXml->setDocumentElement( '/POWER
+MART/REPOSITORY/FOLDER' );
                              
                              for my $TgtNode (@TargetNode)
                                   {
                              for my $node (@MappletNode) 
                                    {

                                               $TgtNode->addChild( $no
+de );
                                               $TgtNode->setOwnerDocum
+ent( $TargetXml );
                                               #$MpltXml->toFile($OutF
+ileName);
                                               print "The Value is $Tg
+tNode";

                                               
                                               
                                               
                                     }
                                     }
                                
                           }
              }
       close(GET_MAPPLET_LIST);
   
   }
[download]

Sorry, but teaching how the DOM works and how to apply the methods is far beyond what I can do for you.

Your proposed code seems to confuse the source and destination. At least to me it appears that you are taking the elements of the target document and the elements you want to copy to the target document. ->setOwnerDocument needs to be called on nodes that have been removed from another document. Most likely, this would be called on nodes from your source document and not nodes in your target document.