> I'm enhacing the security.fdb database following Ivan Prenosil's
> advices described in Helen Borrie's book.
> I'm going to use GroupId field to distinguish among different groups
> of users and Privilege field to establish a hierarchy in each group.
> May I freely use these apparently unused fields with no side effects ?

Forget it. In Firebird 2
- many of those enhancements are already standard part of Firebird,
and, more importantly to you
- you can't directly connect to security database any more

Ivan
http://www.volny.cz/iprenosil/interbase/