Re: satisfies algorithm

"David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message news:vJ6dnRSku8yechfVnZ2dneKdnZydnZ2d_at_giganews.com...
> "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> news:92kik.14667$cW3.1512_at_nlpi064.nbdc.sbc.com...
>>
>> Yes. Normalize. A schema that is in BCNF does not have any nontrivial
>> functional dependencies where the determinant is not also a key. Where
>> there is a key, there should also be a unique index of some sort, making
>> it impossible for there to be two tuples with the same determinant.
>>
>
> Unique indexes have nothing to do with keys. A key is a logical construct
> whereas an index is merely one possible physical structure used by some
> DBMSs. A key does not require an index.

Keys have the uniqueness property. Don't you agree that the uniqueness property should be enforced by whatever implementation is chosen? I think you would be hard pressed with today's technology to find a more efficient implementation method to enforce the uniqueness property than maintaining an index--especially when a relation has more than one key. Received on Sat Jul 26 2008 - 15:12:15 CEST