Solved

DB Tables which are in 3NF or 4NF but not in DKNF

Posted on 2009-04-08
3
817 Views
Last Modified: 2013-12-25
Are there examples of Relational tables which are in 3NF or 4NF but not in Domain Key Normal Form?
0
Comment
Question by:dtivmk
  • 2
3 Comments
 
LVL 22

Accepted Solution

by:
dportas earned 500 total points
Comment Utility
Yes. DKNF is unlike other normal forms because it is concerned with constraints rather than purely FDs, MVDs and JDs. A relation schema is in DKNF if all its constraints are equivalent to its key and domain constraints only. According to Fagin (who invented DKNF) a DKNF schema is automatically in 5NF but a 5NF schema is not necessarily in DKNF.

A trivial example of a relation in 5NF but not in DKNF is:
R{A,B} KEY {A,B}
with an inclusion dependency between A and B. In other words the constraint is:
project{A}( R ) = project{B}( R )

This constraint isn't implied by the key {A,B} therefore R is not in DKNF.
0
 
LVL 22

Expert Comment

by:dportas
Comment Utility
I thought of an even neater example:

P {A}
constraint: SUM(A)< 10

ie. The sum total of A must be less than 10
0

Featured Post

IT, Stop Being Called Into Every Meeting

Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

Join & Write a Comment

Creating and Managing Databases with phpMyAdmin in cPanel.
Although it can be difficult to imagine, someday your child will have a career of his or her own. He or she will likely start a family, buy a home and start having their own children. So, while being a kid is still extremely important, it’s also …
Viewers will get an overview of the benefits and risks of using Bitcoin to accept payments. What Bitcoin is: Legality: Risks: Benefits: Which businesses are best suited?: Other things you should know: How to get started:
This tutorial will teach you the core code needed to finalize the addition of a watermark to your image. The viewer will use a small PHP class to learn and create a watermark.

744 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now