Re: identity columns

If an e-mail address is going to be a PK at all, it should be the PK of an inbox. Inboxes are distinct entities from persons, like employees. When you use an e-mail address to identify an employee you have used an attribute of a different entity, although a related one. Conceptual modeling precepts tell you to stay away from this.

I think that's a good warning in this case. The relationship between inboxes and persons is too transient to count on it.

Others have said almost the same thing already.

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Regards,
    David Cressey
    www.dcressey.com