> Suppose you take the advice of this article, and use, say, social security numbers to identify people.
You seen to have misunderstood the point of the article: the author is recommending NOT using the SSN (a natural key) for primary keys, and instead to use an artificial, automatically generated key, so that the SSN is decoupled from the record and can potentially be updated.
But SSN's are artificial, automatically generated keys. They are not natural keys, they cannot be natural keys for persons, because not every person has one.
A natural key is a set of attributes which an entity has even if it is not in your database.
You seen to have misunderstood the point of the article: the author is recommending NOT using the SSN (a natural key) for primary keys, and instead to use an artificial, automatically generated key, so that the SSN is decoupled from the record and can potentially be updated.