requires-vs-attribute

test.pl

package My::Role::Owned;
use Moose::Role;

requires 'owner';

package My::Role::Owned::FromFile;

use Moose::Role;
with 'My::Role::Owned';

has 'owner' => (
    is => 'ro',
    builder => '_build_owner',  
);

has 'file' => (
    is => 'ro',
    required => 1,
);

sub _build_owner {
    ... # detect owner from file owner
}