Re: Negative Numbers in "Identity" or" Autonumber" fields

From: Bernard Peek <bap_at_alpha.shrdlu.com>
Date: 21 Mar 2007 20:19:04 GMT
Message-ID: <slrnf034f8.9tl.bap@alpha.shrdlu.com>

On 2007-03-21, Marshall <marshall.spight_at_gmail.com> wrote:

>

> It leaves me somewhat puzzled, because
> it appears to have use but it doesn't appear to do anything.
> In the RM world it can function as a surrogate. I also
> run into this is security papers. "An unforgeable token"
> is what it is usually called in security land. I vaguely
> recall it had other uses but I don't offhand remember
> what they are.

It does have a purpose but you have to take a wider view of database "systems." The identity maps to real-world objects, there is a 1:1 relationship but it isn't enforced by the computer. It's up to the system designer to put mechanisms in place to make sure that "the system" as a whole keeps track of the mapping.

One thing to be clear on though. There is only one operator but it's not "=" in the arithmetic sense. It's "=" in the "is the same thing as" sense. In programming languages you can have two variables that have the same value, without necessarily being the same thing.

There isn't any computerised representation of the value because the identity isn't restricted to a particular language, alphabet or representational system. I can refer to "my car" or "my automobile" and mean the same thing. A Frenchman might use a completely different sequence of characters but all of these character strings are labels attached to the identity, not the identity itself.

-- 
bap_at_shrdlu.com
In search of cognoscenti

Received on Wed Mar 21 2007 - 15:19:04 CDT