package NVC::DB::User;
  our @ISA = qw/ NVC::DB /;
  use NVC::DB::attr qw/ cache /;
  ...

##</code><code>##

  @NVC::DB::cache::User::ISA = @NVC::DB::User::ISA;
  @NVC::DB::User::ISA = qw/ NVC::DB::cache::User /;