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Re: Sixth normal form

From: Jan Hidders <hidders_at_gmail.com>
Date: Mon, 30 Jul 2007 09:30:30 -0700
Message-ID: <1185813030.422971.126780@k79g2000hse.googlegroups.com>


On 30 jul, 12:45, Sameeksha <sameeksha.ch..._at_gmail.com> wrote:
> Googling out for definition and explanation for sixth normal form only
> resulted in the following information - "6th normal form states that a
> relation R should not contain any non-trivial join dependencies". Also
> everywhere it is stated that this normal form takes into account the
> temporal (time) dimension to the relational model, and that current
> implementations like SQL server 2005 do not implement this normal
> form.

It would help if you first explained what you already know, so we don't spend time on explaining what you already know. Do you know what at join dependency is? Do you know when it is trivial?

Btw. where and in what context did you read that SQL server did not support this normal form? That is a rather odd statement since the normal form is just about how much to split your relations into projections, so strictly speaking it needs no support at all form the DBMS. But perhaps support for temporal features was meant?

> Any more explanation and preferably an example would help in
> understanding the concept behind this normal form.

Informally put it says that every distinct fact gets its own relation or "if you can split, then you should". So if you have a relation Student(student_id, name, address) then the fact that the student with a certain id has a certain name is split form the fact the this student lives at a certain address. This is different from 5NF since there you only split when there is a risk of redundancy or update anomalies.

Received on Mon Jul 30 2007 - 11:30:30 CDT

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