Re: satisfies algorithm

From: Brian Selzer <>
Date: Sat, 26 Jul 2008 23:22:02 -0400
Message-ID: <wRRik.17363$>

"David Portas" <> wrote in message
> "Brian Selzer" <> wrote in message
> news:PoFik.34002$
>> "David Portas" <> wrote in message
>>> "Brian Selzer" <> wrote in message
>>> news:92kik.14667$
>>>> 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?
> Yes of course.
>> 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.
> This is a different thing from saying there "should" be a unique index for
> a key. Some DBMSs don't even have the concept of indexes (Netezza comes to
> mind). Whether a database has indexes or not has nothing to do with
> whether keys are enforced.

In nearly all of the commercial implementations and implementations of systems built with commercial implementations that pervade the industry, where there is a unique constraint or a primary key constraint that needs to be enforced, there is also an index. But thank you for pointing out that there are alternatives to using indexes without also providing the algorithms for those alternatives for the OP's edification. In other words, "where's the beef?" Can you back up your claims with more than marketing hype? I read the white papers Netezza provided on their web site, but I didn't feel a thrill going up my leg, if you know what I mean. Can you provide links to academic papers that describe these alteratives in detail. I'm curious, and I would bet that others here are too.

By the way, how Netezza is implemented internally is anyone's guess. They may sort active domains--storing them in a particular order. Who knows? but wouldn't that be similar enough to be considered a facsimilie of an index?

--Brian Received on Sat Jul 26 2008 - 22:22:02 CDT

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