Re: Surrogate primary key plus unique constraint vs. natural primary key: data integrity?

Cimode wrote:

> Any theory is nothing but natural, including relational theory.

Huh? Is that what you intended to write? That makes no sense as it stands.

>> value assigned outside the enterprise of interest that is a key >> used within it is "natural".

> An *enterprise of interest* does not say anything about the fact
> that a surrogate key may at some future point in time be considered a
> natural key.

The enterprise of interest (EoI) doesn't "say" anything, ever. It is merely the context for a conceptual model. The EoI is whatever my customer/user tells me it is. If my customer tells me he is given some information and I am satisfied it uniquely determines an entity in his EoI then it is a natural key in his EoI. There really is no room to argue that it is not.

> But the point is that subjectivity can not be taken from
> the equation in any scheme involving establishing a unique identifier.

I think you have abbreviated this argument excessively. I really don't see your point.

>> A credit card number is a synthetic/surrogate key in the card issuer's >> database but it's a natural key in the merchant's database.

> See above.

See what above? And why? Your brevity borders on cryptic.

> Explaining distinguishibility seems a more important challenge

Another cryptic squib. What is challenging about it?

-- 

Roy