You've got quite a few problems here: $class not used in new(); $parser leaps into existence in new(); $parser->parsefile(...); seems to be in totally the wrong place; no connection between new() and startElement(); and others.

Without hacking your code around too much, I'd probably change:

 bless $self;

 ## now, set up XML::Parser;
 $parser->parsefile ("/path/to/some/file/$id.xml");
 return $self;
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to

    bless $self, $class;

    $self->init();

    return $self;
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with init() looking something like:

sub init {
    my $self = shift;
    my $id = $self->{id};

    # Parse the "$id.xml" file here
    # Get the $property value

    $self->{property} = $property;

    return;
}
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You'd be well advised to put use strict; and use warnings; at the top of your code.