Normalization of classes

Created November 8, 2009
Last updated November 8, 2009

[ Japanese | English ]

  In this page , I will explan the normalization ^{1 2} of classes ( especially entity classes )³.
  The entity classes is the classes managing datas.
  When you create the class diagram, I think that you pay attention to the module cohesion and coupling.
At this time, When you normalize classes, new classes are likely extracted.

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Note.
1:"normalization" is the same means as the normalization in RDB.
2:The normalization is a range of the Fundamental Information Technology Engineer Examination (FE) , the Software Design amp; Development Engineer Examination (SW) , the Database Systems Engineer Examination (DB) and so on of the Japan Information-Technology Engineers Examination. If you aim at passing , study it.
3:There are rew websites and books about object-oriented. I doubt that the authors of them understand object-oriented.

1. What is the normalization?
2. Example of the normalization
3. Reference

1. What is the normalization?

  The normalization of the datas is the unification and integration of datas.   If you normalize datas , you can prevent datas not being adjusted, and lose the redundancy.

  If you want to know the detail of the normalization , please refer to 1 of Reference.
Note:There is regularization from the 1NF to the 6NF. But you understand enough to from the 1NF to the 3NF.

  Attention: There are the difference of the idea between RDB and object-oriented. For instance, assosication (see "Class diagram , Entity-relationship diagram and Extraction of the class") and operation (entity in RDB doesn't have it).

2. Example of the normalization

The following is examples. (Attention: "*" of "*NF" is posibility mistake.)

Aggregation and Composition
The aggregation and composition is result of 1NF( First Normal Form ).
Flyweight pattern
I think that this class is extracted by 2NF or 3NF.

3. Reference

  In this page , I explained only really easily for the regularization of datas.
  If you need , see the website at the following table.
  I think that you should understand from the 1NF to the 3NF.

No.	Linked Website Name	Description	Linked date
1	Database normalization - Wikipedia, the free encyclopedia	This web site explains normal form.	November 8, 2009
2	Introduction to Class Normalization	This web site explains normal form of classes.	November 8, 2009

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