Gerhardus,

> You mentioned that this method is maybe obsolete. Can you tell me what
> the new way of doing this is.

Surrogate keys and unique IDs; no composite keys.

> Or the correct way in firebird/ib to do
> this without performance degradence.

With IB it is more healthy to avoid defining foreign keys on low
selectivity columns; it depends on the nature of your m/d relationship.
I'd tend to use one in your case.
Ciao
--
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_/\/ando