On 05/03/2011 12:51 PM, Jeff Davis wrote:
On Mon, 2011-05-02 at 20:06 -0600, Rob Sargent wrote:
Jeff Davis wrote:
In particular, I think you are falsely assuming that a natural key must
be generated from an outside source (or some source outside of your
control), and is therefore not reliably unique.
You can generate your own keys...
...
My wife works (at the sql level) with shall we say "records about
people". Real records, real people. Somewhere around 2 million unique
individuals, several million source records. They don't all have ssn,
they don't all have a drivers license. They don't all have an address,
many have several addresses (especially over time) and separate people
have at one time or another lived at the same address. You would be
surprise how many "bob smith"s where born on the same day. But then
they weren't all born in a hospital etc etc etc. A person may present
on any of a birth record, a death record, a hospital record, a drivers
license, a medical registry, a marriage record and so on. There simply
is no natural key for a human. We won't even worry about the
non-uniqueness of ssn. And please don't get her started on twins. :)
I can only imagine that other equally complex entities are just as
slippery when it comes time to pinpoint the natural key.
I think you missed my point. You don't have to rely on natural keys that
come from somewhere else; you can make up your own, truly unique
identifier.
Regards,
Jeff Davis
Sorry, but I'm confused, but that's common. Isn't a "natural key" to be
compose solely from the attributes of the entity? As in a subset of the
columns of the table in a third-normalish world. Isn't tacking on
another column with a concocted id joining the "pervassiveness"?
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