Relational databases and databases

Relational databases and databases

A relational database is a database created on the basis of a relational model. It processes data in a database using mathematical concepts and methods such as set algebra.

A relational database is a two-dimensional table model. Therefore, a relational database is a data organization composed of two-dimensional tables and their relationships. A relational model consists of three parts: relational data structure, relational operation set, and Relational integrity constraint.

A table is a set of data organized in the form of rows and columns. A database contains one or more tables. For example, there may be a table named authors about the author information. Each column contains information of a specific type, such as the author's last name. Each line contains all information about a specific Author: name, address, and so on. In a relational database, a table is a link. A relational database can contain multiple tables.

Link: it can be understood as a two-dimensional table. Each link has a relational name, that is, the table name.

Tuples: a row in the orders table, which is often called a record in the database.

Attribute: it can be understood as a column in the tables Table, which is often called a field in the database.

Field: The value range of the attribute, that is, the value limit of a column in the database.

Keywords: A group of attributes that can uniquely identify tuples. A database is often called a primary key and consists of one or more columns.

12 principles

The relational system should fully support all features of the relational model. Criterion 0

A relational database management system must be able to manage databases through its relational capabilities.

Criterion 1

Information Standards all information of the relational database management system should be explicitly expressed with the value in the table at the logic level.

Criterion 2

Ensure that the access rules rely on the combination of the table name, master code, and column name to ensure that each data item in the relational database can be accessed logically.

Criterion 3

The relational database management system supports the concept of null values and uses a systematic method to process null values.

Criterion 4

The description of a dynamic online data dictionary database based on a relational model adopts the same logic level as that of common data.

Criterion 5

A unified data sub-language a relational database management system can have several languages and multiple terminal access methods, but must have one language. Its statements can be expressed as strings specified by strict syntax, and fully supports various rules.

Criterion 6

All theoretically updatable views of the view update criterion should also be updated by the system.

Guideline 7

Advanced insert, modify, and delete operations should be optimized for query.

Criterion 8

The physical independence of data no matter whether the database data changes in the storage representation or access method, the application and terminal activities remain logically unchanged.

Criterion 9 Data logic independence when the theoretical information of the basic relationship is not damaged, the application and terminal activities remain logically unchanged.

Guideline 10

Integrity constraints of data integrity relational databases must be defined in the database language and stored in the data dictionary.

Guideline 11

The distributed independent relational database management system keeps the logic unchanged when introducing distributed data or data redistribution.

Guideline 12

Non-destructive rules if a relational database management system has a low-level language, this low-level language cannot violate or bypass the integrity rules.