Claudio,

> > To further confuse, people coming from desktop dbs often think a
> > key and an index are the same thing. They are not. It so
> > happens that one of the things IB does to implement its rules for
> > a primary key is to create a unique, non-nullable index for its
> > column(s). Currently, it implements its rules for a foreign key
> > by creating a non-unique, non-nullable index for it's column(s).
>
> I either misunderstood the posting or there's a typo here. FKs are supported
> by an underlying index that's non-unique, so it accepts NULL entries.
> Otherwise, you couldn't create non-mandatory, non-identifying relationships
> between entities (tables).

A typo for sure; there's no such thing as a "non-nullable index".
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