6th normal form

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NovRain8
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6th normal form

Post by NovRain8 »

Hi, i need help from someone who can explain what the 6th normal form is how it proceeds from the 5th normal form, as it is written in "temporal data and the relational model" by Hugh Darwen thanks
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Chris Corbyn
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Post by Chris Corbyn »

School/University question? :P

http://www.tonymarston.co.uk/php-mysql/ ... n.html#6nf
6th (Domain-Key) Normal Form

A table is in sixth normal form (6NF) or Domain-Key normal form (DKNF) if it is in 5NF and if all constraints and dependencies that should hold on the relation can be enforced simply by enforcing the domain constraints and the key constraints specified on the relation.

Another way of expressing this is:

... if every constraint on the table is a logical consequence of the definition of keys and domains.

1. An domain constraint (better called an attribute constraint) is simply a constraint to the effect a given attribute A of R takes its values from some given domain D.
2. A key constraint is simply a constraint to the effect that a given set A, B, ..., C of R constitutes a key for R.
NovRain8
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Post by NovRain8 »

yeah, doing this for a project :) there's another definition about 6nf where it says that : "A relvar R is in 6NF if R satisfies no nontrivial join dependencies at all", is this the same as the one in the link and what does this definition mean?


thanks for the help
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Chris Corbyn
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Post by Chris Corbyn »

No clue :? I've only ever studied up to 4NF (just self-study).

I'm intrigued now though so I shall sift through some books and see if I can find a *good* explanation of it, preferrably with an example.
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Chris Corbyn
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Post by Chris Corbyn »

DKNF is apparently not the actual 6NF, which you're talking about :(

6NF was created in 2005 and as such isn't used yet, from what I've read. I can't find anything out on it given how new it is so I can't really help you i'm afraid.

If you do find anything please let us know :)
timvw
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Post by timvw »

The only implementation i've seen untill now looks as following:

- Each property (apart from the PK) is saved in it's property_table (PK, timestamp, value).

http://www.cs.man.ac.uk/img/TIME-2002/darwen-time02.pdf
NovRain8
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Post by NovRain8 »

ic, was wondering how it follows from 5th normal form, which i don't quite understand the part about join dependcies and if the join dependency is trivial
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