Asynchronous notifications

Hi hackers,
I've dived into the jdbc QueryExecutor code to see how Notifications
are handled. Notifications are handled into the execute() method. In
this method, return from pg_stream is read after SendQuery() method is
called. My quite is quite "architectural". I would like to know the
reason that makes the final user to perform a query to get notifications
from the server. My question is directly linked to my problem : I would
like to avoid in my client code to have a thread executing (so sending
packets) SQL void string commands each n seconds in order to notify
observers or other classes. So do you think it is possible do have a
solution with pg JDBC driver? How can I do this? Does JDBC conformance
tests does allow this?

Thanks in advance!
--
Jean-Christophe Arnu (arnu {at,arobase} paratronic {dot,point} fr