Ideally I'm looking to set a single value in a database once and once only (at the system level) and then be able to retrieve that value as a constant within before insert triggers. (such as a SITEID integer).

e.g. similar to using TODAY or CURRENT_USER,
though I realise this is a user-defined value.
Being able to extend RDB$SET_CONTEXT()
(within the SYSTEM namespace) would have been ideal.

Does anyone know if this is possible or if not I'm assuming people select from a control table row (or a.n.other suggestion?).
Tom