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normalization estate exercise Expand / Collapse
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Posted Wednesday, August 6, 2014 6:04 AM
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pietlinden (8/5/2014)
How can you get to 3NF if you don't go through 1NF and 2NF first?


Very easily, you just need to ensure that the non-trivial determinants of every non-key attribute are superkeys. Outside of an academic exercise I'm surprised if anyone would go through the trouble of creating a table design that satisifies 1NF but not 2NF and then refine it to make it satisfy 2NF and then refine it again to make it 3NF. I've certainly never bothered with such exercises outside the classroom.

2NF and 3NF are of mostly historical or academic importance anyway. Most of the time it makes sense to design to Boyce-Codd / 5th Normal Form and don't concern yourself with 3NF except in cases where you need to denormalize in order to enforce certain business rules.



David
Post #1600180
Posted Wednesday, August 6, 2014 6:11 AM


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sqlvogel (8/6/2014)
pietlinden (8/5/2014)
How can you get to 3NF if you don't go through 1NF and 2NF first?


Very easily, you just need to ensure that the non-trivial determinants of every non-key attribute are superkeys.


Which is fine when you're comfortable with normalisation and know what you're doing. The OP however is just learning it and doing an academic exercise.



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Post #1600187
Posted Wednesday, August 6, 2014 6:34 AM
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sqlvogel (8/6/2014)
pietlinden (8/5/2014)
How can you get to 3NF if you don't go through 1NF and 2NF first?


Very easily, you just need to ensure that the non-trivial determinants of every non-key attribute are superkeys. Outside of an academic exercise I'm surprised if anyone would go through the trouble of creating a table design that satisifies 1NF but not 2NF and then refine it to make it satisfy 2NF and then refine it again to make it 3NF. I've certainly never bothered with such exercises outside the classroom.

2NF and 3NF are of mostly historical or academic importance anyway. Most of the time it makes sense to design to Boyce-Codd / 5th Normal Form and don't concern yourself with 3NF except in cases where you need to denormalize in order to enforce certain business rules.



Although it moves very quickly, I still think in terms of 1st, 2nd and so forth. That way I know I have approached it correctly. Only with the simplest databases would I be comfortable with moving directly to BCNF. And, even then, I think my mind would still go through the earlier stages.

Tom
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Posted Wednesday, August 6, 2014 6:37 AM
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For the OP:

Here is a link with a straightforward explanation of the normal forms.

http://databases.about.com/od/specificproducts/a/normalization.htm

You should be able to create the 1st and 2nd normal forms from that explanation.

Tom
Post #1600200
Posted Wednesday, August 6, 2014 6:58 AM
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OCTom (8/6/2014)
For the OP:

Here is a link with a straightforward explanation of the normal forms.

http://databases.about.com/od/specificproducts/a/normalization.htm

You should be able to create the 1st and 2nd normal forms from that explanation.

Tom

"Straightforward" but also completely WRONG. Ignore it. Don't waste time reading anything on about.com.


David
Post #1600211
Posted Wednesday, August 6, 2014 12:06 PM
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if its the usually unf to 3nf its very easy but my school have their own method and if its difficult I will be glad but its impossible some times.


this are the rules..

Un-normalised Form – UNF: Transfer all identifiable attributes from the sample to a list ensuring each attribute has a unique name; structure the list according to the repeating groups (a repeating group is defined as any group of one or more attributes which has [regular sets of] multiple values for a single value of the initial key); choose an initial key for the RDA

First Normal Form – 1NF: Separate into new relations each repeating group, generating appropriate keys for each relation: this means choosing a key for the group and propagating (copying) the key of the relation from which the group was separated as part of the key of the new relation; any single-valued attributes remain with the initial key

Second Normal Form – 2NF: Separate into new relations any attributes dependent on only part of each compound key along with their non-key attribute(s); the original compound keys are left intact (along with any dependent attributes)


Third Normal Form – 3NF:
Separate into new relations any attributes dependent on other non-key attributes along with their key attribute(s); foreign keys are retained in the original relation
Check compound keys for any redundant parts – if any part of a compound key can be determined by the rest of the key, demote the attribute(s) to non-key status (these may also be foreign keys)


...could be easy in theory
Post #1600343
Posted Tuesday, August 12, 2014 10:21 PM
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This exercise is a lot easier to understand if you have some data to work with. It's easier to see repeating fields if you have a table structure. The usual dead giveaway is the fact that each repeating column ends with a subscript (a number).... e.g. Toxicity1, Toxicity2, ... etc.
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