private void cleanup() {
Session s = openSession();
Transaction txn = s.beginTransaction();
// workaround awesome HSQLDB "feature"
s.createQuery( "delete from Animal where mother is not null or father is not null" ).executeUpdate();
s.createQuery( "delete from Animal" ).executeUpdate();
s.createQuery( "delete from Zoo" ).executeUpdate();
s.createQuery( "delete from Joiner" ).executeUpdate();
s.createQuery( "delete from Vehicle" ).executeUpdate();
s.createQuery( "delete from BooleanLiteralEntity" ).executeUpdate();