On Jan 19, 2006, at 10:34 , Dann Corbit wrote:
http://www.db.ucsd.edu/cse132B/Thirdmanifesto.pdf
"PROPOSITION 1.4: Unique Identifiers (UIDs) for records should be
assigned by the DBMS only if a user-defined primary key is not
available.
<snip />
An immutable primary key has an extra advantage over a system-
assigned unique identifier because it has a natural, human readable
meaning. Consequently, in data interchange or debugging this may be
an advantage. If no primary key is available for a collection,
then it is imperative that a system-assigned UID be provided.
<snip />
Dann Corbit:
The primary key should be immutable, meaning that its value should
not be changed during the course of normal operations of the
database. What natural key is immutable? The answer is that such
an attribute does not exist. To use them for such a purpose is
begging for trouble.
As far as I can tell, the only difference between your position,
Dann, and Date and Darwen's, is that you think no natural key is
immutable. If you *could* find an immutable natural key, would it be
an acceptable key for you? Date and Darwen say explicitly that if no
immutable (natural) (primary) key is available a system-assigned UID
is required. If you think there is no immutable natural key
available, Darwen and Date would agree that you should use a system-
generated key. Or do you think I'm misreading you or The Third
Manifesto?
Michael Glaesemann
grzm myrealbox com
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