First paradigm, second paradigm, and third paradigm

Source: Internet
Author: User
If all attributes of a relational model R are basic data items that cannot be divided, then R1NF (that is, R conforms to the first paradigm ). Two points: 1. Each field can only store two values for a single value course, which does not conform to the first paradigm. The following can be changed: 2. Each record must be identified using a unique primary key.

If all attributes of a relational model R are basic data items that cannot be divided, then R1NF (that is, R conforms to the first paradigm ). Two points: 1. Each field can only store two values for a single value course, which does not conform to the first paradigm. The following can be changed: 2. Each record must be identified using a unique primary key.

First paradigm, second paradigm, third paradigm, first paradigm

If all the attributes of a relational model R are basic data items that cannot be divided, then R is 1NF (that is, R conforms to the first paradigm ).

Two points:

1. Each field can only store a single value

The course has two values, which do not conform to the first paradigm and can be changed as follows:

2. Each record must be identified by a unique primary key.

Duplicate groups appear here, which also does not meet the first paradigm. Because of the lack of a unique identifier code, you can change it

Second paradigm

If the relational model rε 1NF (that is, R conforms to the first paradigm) and every non-primary attribute is completely dependent on the R code, rε 2NF (that is, R conforms to the second paradigm ).

The table code here is (student ID, course). You can determine the system name, dormitory, and score, or the three items depend on the first two items.

The full score (student ID, course) is dependent on the department name (student ID, course), that is, you can determine the Department name by knowing the student ID or course. part of the dormitory building depends on (student ID, course), that is, the dormitory building can be determined by knowing the student ID or course.

Because the non-primary attribute is named, the dormitory building is not completely dependent on and code, and does not conform to the second paradigm. You can change it

Table 1

Third paradigm

If the relational mode rε 3NF (that is, R conforms to the third paradigm), neither the Code nor the code is partially dependent on each non-primary attribute.

The above table 2 does not conform to the third paradigm. This is because you know the system name, and you also know the dormitory building. The dormitory building transmission relies on code (student ID) and can be divided

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