MellioWellio
Programmer
I have experience working with data in 3NF, but my knowledge of normalization stops there. Please could anyone explain them to me in simple terms? It would be much appreciated!!! 
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BCNF, 4NF, 5NF 1
- Thread starter MellioWellio
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3NF is the standard for database normalization. You can normalize to the 4th and 5th forms, but most developers don't. For example, zip codes could potentially be its own table, using a FK from the ZipCode table to the Address table, but how often do ZipCodes actually change? Is there a valid reason for breaking the ZipCode out of the address? Usually not. As long as you have normalized to the third form, you should be fine.
Leslie
Anything worth doing is a lot more difficult than it's worth - Unknown Induhvidual
Leslie
Anything worth doing is a lot more difficult than it's worth - Unknown Induhvidual
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johnherman
MIS
Here's an example of a 4NF problem as presented in Teorey's book.
Consider the entities Employee, Skill, and Project. An employee must have all skills required for the project to work on a project. Thus there is a relation or bridge table Employee-Skill-Project. However, the Employee-Skill relationship remains regardless of the project and the employee can have skills not related to the project. The composite relation or bridge tables are Employee-Skill, Project-Skill, and Employee_Project, but this is not enough as an employee may require several skills or have worked on several projects. A model is in 4NF if all many-to-many-to-many relationships can only be decomposed into 3 many-to-many relationships.
I'm not even going to attempt to explain 5NF in this forum - sorry.
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The reasonable man adapts himself to the world. The unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. - George Bernard Shaw
Consider the entities Employee, Skill, and Project. An employee must have all skills required for the project to work on a project. Thus there is a relation or bridge table Employee-Skill-Project. However, the Employee-Skill relationship remains regardless of the project and the employee can have skills not related to the project. The composite relation or bridge tables are Employee-Skill, Project-Skill, and Employee_Project, but this is not enough as an employee may require several skills or have worked on several projects. A model is in 4NF if all many-to-many-to-many relationships can only be decomposed into 3 many-to-many relationships.
I'm not even going to attempt to explain 5NF in this forum - sorry.
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The reasonable man adapts himself to the world. The unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. - George Bernard Shaw
- Thread starter
- #4
MellioWellio
Programmer
johnherman - thanks for the definition of 4NF, i think ive grasped it. Found a definition of BCNF and 5NF on another site too, so no ned to explain in this forum. Thanks again
johnherman
MIS
MellioWellio -
Would you please post your link to the other site here or write a FAQ regarding 4NF and 5NF?
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The reasonable man adapts himself to the world. The unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. - George Bernard Shaw
Would you please post your link to the other site here or write a FAQ regarding 4NF and 5NF?
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The reasonable man adapts himself to the world. The unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. - George Bernard Shaw
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