Re: Beginner help needed in database design

On Wed, 2 Feb 2005 11:00:16 -0700, "Mark A" <nobody_at_nowhere.com> wrote:

>"Ed Stevens" <nospam_at_noway.nohow> wrote in message
>news:na22015ej7odbn2144icl74gm8tjpp17st_at_4ax.com...
>> The phrase "even in ..." implied (to me) that you were saying these
>> concepts didn't exist at all .... *even in* relational db's. You
>> said nothing about referential integrity in that paragraph, unless
>> that was what you meant by saying that "primary *and* foreign keys did
>> not exist" (emphasis on the "and") While true that referential
>> integrity -- whether enforced by the dbms or the app -- require
>> primary and foreign keys (however implemented) it does not follow that
>> implementation of a primary key necessarily implies the existence of
>> either foreign keys or RI. It seems to me that a unique index -- or
>> any mechanism that forces a particular column/field to be unique --
>> pretty much equates to a PK. At least as long as you only have one
>> such unique index on a particular data store.
>>
>> But we quibble over historical nits.
>> Thanks.
>>
>> - Ed Stevens
>>
>
>I misspoke when I said "even". I should have said "primary and foreign keys
>did not exist in relational databases" prior to about 1988.
>
>Foreign keys do not exist in VSAM, so it does not have referential
>integrity, even if it does have unique indexes.
>
>If just having unique indexes constituted "referential integrity" then
>Primary Keys and Foreign Keys would not have been added to relational
>databases about 1988 (and the ANSI standard for SQL).
>

Agreed.

And if it looked like I was trying to pick you apart please accept my apology. What may have looked that way was really just an attempt to explain why I understood your posting the way I did. Then, over lunch, I began to see how my explanation could be read to have an antagonistic tone. None intended. And such is often the weakness of the written word.
Thanks.

• Ed Stevens

Cohn's Law: The more time you spend in reporting on what you are doing, the less time you have to do anything. Stability is achieved when you spend all your time doing nothing but reporting on the nothing you are doing. Received on Wed Feb 02 2005 - 12:37:45 CST