Three Paradigms of database

Three Paradigms of database

2015-05-19

13 informal description of the paradigm
23 Paradigm Interpretation
33 Paradigm Examples

13 informal description of the paradigm

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• 1NF: field is not divided;
• 2NF: There is a primary key, the non-primary key field is completely dependent on the primary key, so-called full dependency refers to the existence of only the main key to rely on a part of the property (mainly for the Federated primary Key);
• 3NF: Non-primary key fields cannot depend on each other;

23 Paradigm Interpretation

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• 1NF: Atomic field can not be re-divided, otherwise it is not a relational database;
• 2NF: Uniqueness A table shows only one thing;
• 3NF: Each column is directly related to the primary key, there is no transitive dependency;

33 Paradigm Examples

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3.1 First Paradigm

Table 1 Examples that do not conform to the first paradigm (create a table in a relational database)

Field 1

Field 2 (Field 2.1, field 2.2)

Field 3

......

The problem: Because the design does not have such a table, so there is no problem;

3.2 Second Paradigm

Table 2 Examples that do not conform to the second paradigm:

School Number

Name

Age

Course Name

Results

Credits

Because the students have many courses, the school number and the course name as the joint primary key of the table. The name and age of the table depend only on the attribute number of the primary key, and the grades and credits depend only on the attribute course name of the primary key, which does not conform to the second paradigm.

This table clearly illustrates two transactions: Student information, course information;

A problem exists:

• Data redundancy, each record contains the same information;
• Delete exception: Delete all student scores, the course information is completely deleted;
• Insert exception: The student does not choose the class, cannot record into the database;
• Update Exception: Adjust course credits and all lines are adjusted.

Correction:

Table 2.1 Students

School Number

Name

Age

Table 2.2 Courses

Course Name

Credits

Table 2.3 Course Selection Relationship

School Number

Course Name

Results

Satisfying the 2nd paradigm only eliminates the insertion exception.

3.3 Third Paradigm

Table 3 examples that do not conform to the third paradigm:

School Number

Name

Age

School of your own

College Contact number

Keyword is a single keyword "study number";

Presence Dependent Delivery: (school number) → (school) → (college location, college phone)

A problem exists:

• Data redundancy: there are duplicate values;
• Update exception: Duplicate redundant information, modify the need to modify multiple records at the same time, otherwise there will be inconsistent data situation
• Delete Exception: The students graduated from the field, will also delete the school information

Correction:

Table 3.1 Students

School Number

Name

Age

School of your own

Table 3.2 College

School of your own

College Contact number

Three Paradigms of database