Database Paradigm (normal form NF), normalnf

Source: Internet
Author: User

Database Paradigm (normal form NF), normalnf

1. Currently, there are six paradigms: 1NF, 2NF, 3NF, BCNF (base-cod paradigm), 4NF, and 5NF (perfect paradigm ).

2. Various paradigms are progressive, backward compatible, that is, to meet the second paradigm, must first meet the first paradigm.

3. The higher the paradigm, the smaller the database redundancy. However, this increases the number of tables, increases the query complexity, and reduces the query performance of the database.

4. 1NF indicates that each attribute cannot be further divided into atoms, such as addresses.

5. 2NF indicates that all attributes in the table must depend entirely on all primary keys, rather than some primary keys (in the case of primary keys associated ). To reduce insert and row exceptions. Completely dependent.

6. 3NF indicates that one attribute depends on all primary keys, while the other depends on this attribute and relies on all primary keys. Although 2NF is satisfied, 3NF is not satisfied. Eliminate passing dependencies.

7. BCNF indicates that, based on 3NF, there is only one candidate key, that is, it acts as the primary key without replacing the key.

8. Generally, it is enough to reach the third paradigm.

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