Relationship Pattern Design Theory and Pattern Design Theory

Source: Internet
Author: User

Relationship Pattern Design Theory and Pattern Design Theory

Normalization:

A low-level paradigm can be transformed into a relational model of several advanced paradigms through Mode Decomposition, that is, normalization.

Paradigm:

Currently, relational databases have six paradigms. The most common ones are the first and third paradigms. The higher the standard, the smaller the data redundancy.

First paradigm: (No score)

The basis of the paradigm. All paradigms must satisfy the first paradigm. Other paradigms are based on the first paradigm.

Second paradigm:

The first paradigm eliminates local dependencies and requires that the attributes of an object fully depend on the primary key.

If local dependency exists, you need to separate this attribute from the part of the candidate key to form a new entity.

Example

(Student ID, name, department, address, course, score );

Exist (student ID, course) --> (name, department, address, score );

It should be divided:

Student ID, course) --> (score)

(Student ID) --> (name, department, address)

Third paradigm:

Eliminate transmission dependencies based on the second paradigm.

Example

(Student ID) --> (name, department, address)

If the same Department address is the same, that is, the address depends on the department, the function dependency does not conform to the third paradigm.

It should be divided:

(Student ID) --> (name, Department)

(Department) --> (address)

After several paradigms are passed down, redundancy and exceptions will be eliminated, that is, the common problems of link pattern design will be eliminated ......


Q: How do I understand the functional dependency part of the database relational model design theory?

Brother, you have the same idea when learning this problem. So I want to give you a bit of my opinion: the reason why you cannot understand the FD reasoning rules is that the basic knowledge related to your database design is incomplete and incomplete. Here, it is like fixing a bug and introducing a new bug. Therefore, we recommend that you study the previous chapter and practice more, in the future, it will be very useful for your programming and development.

What is the difference between the relational model and the relational model in the database?

A link is actually the state or content of the link mode at a certain time point. That is to say, the link mode is a type, and the link is its value. The relational mode is static and stable, while the relational mode is dynamic and constantly changing over time, because relational operations are constantly updating the data in the database. However, in practice, the relationship model and relationship are often collectively referred to as the relationship. Readers can distinguish between them from the context.
Compared with hierarchical and mesh models, it has the following features:
1. Simple data structure (two-dimensional table)
2. solid theoretical basis.
A. Relational Operation Theory
B. Relationship Pattern Design Theory

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