Re: Primary-key ... alternate key ... (newbie question)

Joe, Jan

Thank you for your insites ...

In newbie-language:

The attributes shall be dependend of ALL the key's Nothing else then ALL the key's?

Regards,
Jos

--CELKO-- <71062.1056_at_compuserve.com> wrote in message ...
>>> In many normalisation articles, they sometimes mention to mark the
>alternate
>key's. Why is it important to 'mark' these? Where are they used during
>the normalisation-steps? <<
>
>If a uniqueness relationship exists in your data model, then you must
>show it because it is the truth! That is very simple.
>
>There is a story about the whole PRIMARY KEY thing that we don't like
>to talk about. In his early papers, Dr. Codd created the idea of a
>PRIMARY KEY, which was one of several candidate keys that was picked
>for this honor. Later, he realized that he was still being influenced
>by sequential file systems (think of a magnetic tape), which must have
>a single key that is used to sort the file. All operations in a
>sequential file system depend on (1) sorted order and (2) record
>position within the file. The relational model does not have these
>limits.
>
>The current RM says a key is a key and nobody is special.
>

>>> snipped <<<<
Received on Sun Oct 06 2002 - 09:52:02 CEST