> I'd like to know if someone has already thought about doing this
> with After Update Triggers for the relevant system tables ?

Thinking about it was as far as I ever got.

> Are there any problems with this solution ? e.g. I don't know if
> custom triggers on system tables are restored after a backup &
> restore operation.

As I understand it additional triggers on the system tables should
backup and restore OK.

> I will be happy about any hints, pointers to articles and docs
> (currently I don't know much about system tables but I think this
> could be a good starting point). I guess I'll have to start with
> "System Tables" in the LangRef.pdf.

Sounds like you know where to start. From there its just work :-)

--
Geoff Worboys
Telesis Computing