sub as_hash
  {
    my $self = shift;
    my $name = $self->name;
    my $depth = $self->depth;
    my $id = $self->id;
    return { depth->$depth, id=>$id, name=>$name };
  }

  sub as_flattened_list
  {
    my $self=shift;
    return
      $self->as_hash,
      map { $_->as_flattened_list } $self->sub_cats
  }