Database paradigm? When we edit the relational database, we should design a reasonable relational database, which is called different paradigm, and the higher paradigm is more redundant than the other norm.

Database Paradigm

when designing the relational database, we should design a reasonable relational database to conform to different specifications, and the different norm requirements are called different paradigms, and the higher paradigm database redundancy is lower.

There are currently six paradigms for relational databases: the first paradigm (1NF), the second paradigm (2NF), the third paradigm (3NF), the bath-cod paradigm (BCNF), the fourth normal form (4NF), and the fifth Paradigm (5NF , also known as the perfect paradigm).

First Paradigm (1NF)
The so-called First paradigm (1NF) refers to a specification requirement for domain additions in a relational model, where all domains should be atomic, that is, each column of a database table is an indivisible atomic data item, not a collection, an array, a record, or a non-atomic data item. That is, when an attribute in an entity has multiple values, it must be split into different properties.
The second normal form (2NF) requires that the attributes of an entity depend entirely on the primary key. The so-called full dependency is the inability to have a property that depends only on the primary key, and if so, this part of the property and the primary key should be separated to form a new entity, and the new entity is a one-to-many relationship with the original entity. For the implementation of the distinction, it is common to add a column to the table to store unique identities for each instance. In short, the second paradigm is that on the basis of the first paradigm the property is completely dependent on the primary key.

The third paradigm (3NF) requires that a relationship not contain non-primary key information that has already been included in other relationships. For example, there is a departmental information table, where each department has a department number (dept_id), a department name, a department profile, and so on. After the department number is listed in the Employee Information table, the department name, department profile and other department related information can no longer be added to the Employee Information table. If there is no departmental information table, it should be built according to the third paradigm (3NF), otherwise there will be a lot of data redundancy.

The bath-cod paradigm (BCNF) is a subset of the third paradigm (3NF) that satisfies the bath-cod paradigm (BCNF) must satisfy the third paradigm (3NF). Typically, the bath-cod paradigm is considered to have no new design specifications, but is more demanding in the second and third paradigms, and is therefore considered to be a modified third paradigm, that is, it is actually a correction to the third paradigm, making the database redundant less. This is why BCNF is not called the fourth paradigm. Some books, according to the incremental nature of the requirements of the paradigm call it the fourth paradigm is not normative, but also more difficult to understand the place. The real fourth paradigm, however, is to add the requirements of multiple values and dependencies in the design specification. For BCNF, any true subset of the main code cannot be determined by the main attribute. In relation to the U main code, if any of the true subset X in U cannot be determined by the main attribute y, then the design specification property is BCNF. For example: In the Relationship R, U-Master code, a property is a property in the main code, if there is a->y,y Primary property, then the relationship is not property bcnf. General relational database design, to reach bcnf on it!

From for notes (Wiz)

Database paradigm? When we edit the relational database, we should design a reasonable relational database, which is called different paradigm, and the higher paradigm is more redundant than the other norm.