Ok, sorry :), i am totally new in github and i see a lot of green lines above your comment.

The method gives a functionality that doesn't provide the PDO_INFORMIX but that i think it should be (http://es1.php.net/manual/en/pdo.lastinsertid.php), the only value that i can manage here is a name of a sequence which must be a string, in other case i want delegate the responsibility of the action to the parent code, i think that this is less intrusive.