1 / 21

# Stuff iThink that will be on the Quiz/Midterm. - PowerPoint PPT Presentation

Stuff iThink that will be on the Quiz/Midterm. Fourth Normal Form by Andrew Yee Why 4NF? Performance We want database to take up less space. Why 4NF? To eliminate the possibility for data anomalies. Why 4NF? To reduce the need for: inserts, updates deletes Normal Forms Comparison

Related searches for Stuff iThink that will be on the Quiz/Midterm.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## PowerPoint Slideshow about 'Stuff iThink that will be on the Quiz/Midterm.' - paul2

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

### Stuff iThinkthat will be on the Quiz/Midterm.

Fourth Normal Form

by Andrew Yee

• Performance

• We want database to take up less space.

• To eliminate the possibility for data anomalies.

• To reduce the need for:

• inserts,

• deletes

• Assume X is the Superkey

• “Superkey” still depends on FD’s only.

• Y is not a subset of X

• X and Y are not, together, all the attributes.

• No non-trivial multi-valued dependencies

- Except on superset of a candidate key

- Multi-valued dependencies are functional dependencies.

• Table must be in BCNF

• No Duplications

• Table must be in BCNF

• Assume the table is in BCNF

• The town, Region, and District together form the candidate key.

From Reference #1

• Decomposed into two tables

From Reference #1

Pizza Delivery

From Reference #2

• The table has no non-key attributes because its only key is {Restaurant, Pizza Variety, Delivery Area}.

From Reference #2

Pizza Delivery

From Reference #2

• If we assume, that pizza varieties offered by a restaurant are not affected by delivery area, then it does not meet 4NF.

From Reference #2

Two Non-trivial: MVD

Pizza Delivery

From Reference #2

• The table has two non-trivial multivalued dependencies on the {Restaurant} attribute (which is not a superkey).

• The dependencies are:

• {Restaurant} →→ {Pizza Variety}

• {Restaurant} →→ {Delivery Area}

From Reference #2

Two Non-trivial: MVD

Pizza Delivery

From Reference #2

Varieties By Restaurant

Delivery Areas By Restaurant

No Duplications among rows! Yay!

From Reference #2

• Is this 3NF or BCNF?

• Is this 4NF?

• If not, what are the decomposed tables in 4NF?

Pizza Delivery

• BCNF 2. NO 3. See Below

Delivery Areas By Restaurant

Varieties By Restaurant

No Duplications among rows! Yay!

• Website: Database Design: 4th and 5th Normal Forms « Tod means Fox

URL:http://blog.todmeansfox.com/2007/12/04/database-design-4th-and-5th-normal-forms/

2. Website: Fourth normal form - Wikipedia, the free encyclopedia

URL: http://en.wikipedia.org/wiki/Fourth_normal_form