Mark A wrote:
> "Drago Ganic" <drago.ganic_at_in2.hr> wrote in message
> news:ctom21$ak5$1_at_ls219.htnet.hr...
>
>>Frank,
>>that is simply wrong. Primary key is a integrity constraint! Constraints
>
> are
>
>>logic statements. This has nothing to do with technology. Your and my
>> >>Surname + Name<< are intended to be primary keys for us - bad ones as
>
> we
>
>>know. Threrfore we have SSN etc.
>>
>>Keys are needed for >>identification<< of the other data -- which are for
>> >>description<<.
>>
>>Databases (the relational ones for sure) are data + constraints, not just
>>data! Historically the most used constraints just happen to be primary
>
> (and
>
>>foreign) keys because of the identification problem.
>>
>>Greetings from Croatia,
>>Drago
>>
>
> Primary keys and foreign keys are a DBMS enforced referential constraints.
> Prior to about 1988, primary and foreign keys did not exist, even in
> relational databases (at least not in database that I recall).
>
> Referential integrity can also be enforced by application programs that
> insert, update, or delete data, as it had to be done (if needed) before
> primary and foreign keys were made part of databases.
>
>
BUT since we are discussing the data model here, I am pretty sure Codd
discusses Primary Keys in his work on relational databases. Normalization
rules make no sense without them.
--
Ed Prochak
running http://www.faqs.org/faqs/running-faq/
netiquette http://www.psg.com/emily.html
--
"Two roads diverged in a wood and I
I took the one less travelled by
and that has made all the difference."
robert frost
Received on Sat Feb 05 2005 - 00:44:42 CST
