Re: foreign key constraint versus referential integrity constraint

From: Marshall <>
Date: Sun, 25 Oct 2009 15:05:31 -0700 (PDT)
Message-ID: <>

On Oct 24, 10:53 am, Keith H Duggar <> wrote:


> Anyhow, the question here is not one of our imagination but rather
> simply this: if it makes sense for the RM to support constraints
> on relational /values/ (taken on by variables) why does it not
> make sense to support constraints on relational /expressions/?
> That is a question of general principle not specific design.

This question, it seems to me, is clear and to the point. And I would answer it by saying that we shouldn't really even make the distinction! (At least not formally.)

There are quite a lot of constraint taxonomies out there, and I haven't ever really been able to derive any particular value of any of them. Most generally, ever constraint is a constraint on the entire database; if the constraint mentions only a single variable, then we might say it is a "table constraint" or "relvar constraint" or some such, but that's only a degenerate case of a database constraint. So let us say there is only one type of constraint, the database constraint, and be done with it.

Now that I've said that, let me take it back a bit. Transition constraints don't seem to be quite like anything else. Transition constraints are therefore annoying. :-)

It's Sunday and I'm hot, so I'm posting with reckless abandon. Read my sentences at your own risk.

Marshall Received on Sun Oct 25 2009 - 23:05:31 CET

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