Paradigm Theory, database Paradigm Theory

Paradigm Theory, database Paradigm Theory

Currently, relational databases have six paradigms: 1NF, 2NF, 3NF, 4nf, and 5NF ), the sixth paradigm (6NF ). The paradigm that meets the minimum requirements is the first paradigm. The second paradigm that meets more requirements on the basis of the first paradigm is called the second paradigm, and the rest of the paradigms are in turn. Generally, databases can meet the third paradigm.

The first paradigm is the lowest requirement for Standardization. The first paradigm requires that the data table cannot have duplicate records, that is, there is a keyword. The second requirement of 1NF is that each field cannot be further divided, that is, it has been assigned to the minimum value. The definition of relational database determines that the database meets this condition. The first paradigm is the minimum requirement for designing a database table. Its primary feature is that the attributes of an object cannot be divided. ing to a table means that columns (fields) cannot be divided, as shown below:

Student ID	Name	Contact info
101	Li Xiaofeng	0995-23451214 675423369

The above contact information can be further divided, which does not conform to the first paradigm. We should change it like this:

Student ID	Name	Phone number	QQ
101	Li Xiaofeng	0995-23451214	675423369

Second paradigm:

If a link belongs to 1NF and all the non-primary key fields fully depend on the primary key word, it is called the second paradigm, which is abbreviated as 2NF.

 

 

Name	Talent show Course	Teaching materials
Zhang San	Struts2	Struts2 full manual
Li Si	Struts2	Struts2 full manual
Li Si	Oracle12c	Oracle development manual

The table above conforms to the first paradigm, but the data above shows that the name corresponds to the course of the draft, but the name does not correspond to the teaching material, however, the draft courses are related to teaching materials, so we should design the following table:

Name	Talent show Course
Zhang San	Struts2
Li Si	Struts2
Li Si	Oracle12c

 

Course	Teaching materials
Oracle12c	Oracle development manual
Struts2	Struts full manual

Third paradigm
If a link belongs to 2NF, and each non-Keyword is not transmitted dependent on the primary keyword, this relationship is 3NF. As follows:

Learn well	Name	Class	Department
101	Zhang San	Class C ++ 1	Computer technology
102	Li Si	English Class 1	Foreign language major

The above expression conforms to the second paradigm, but if we already know the class where the student is located, we can also know the department where the student is located, that is to say, additional information is redundant. We have the following designs:

Learn well	Name	Class
101	Zhang San	Class C ++ 1
102	Li Si	English Class 1

 

Class	Department
Class C ++ 1	Computer technology
English Class 1	English Class 1