Some basic concepts in the database __ database

Some important concepts:

① Data: Data is the symbol that describes things. Data is everywhere

② database: The database is where the data is stored. A database is a collection of data and database objects. The so-called database objects are tables, views, stored procedures, triggers, etc.

③ database management System DBMS: A database management system is a computer software used to manage data. The database management system enables users to easily define and manipulate data, maintain data security and integrity, and perform concurrent control and recovery databases under multiple users.

④ Database System DBS: composed of databases, database management systems and users. Broadly speaking, it is composed of computer hardware, operating system, database management system and database application users and maintenance personnel built up under his support.

⑤ Relational Model RM
The relational model is the view that the world is composed of entities and connections
An entity is an object in the real world that has the characteristics or attributes that distinguish it from other things and is associated with other entities. In a relational model, entities are usually represented as tables, each row of a table describes an instance of an entity, and each column of the table describes a feature or attribute of an entity
Contact means the relationship between entities: a pair of one or one pairs, multiple pairs of one

You can use the information of one entity to find information about another entity by contacting
The relational model organizes all the data into a table, which is made up of rows and columns. Rows represent records of data, columns represent fields in records, and tables reflect facts and values in the real world

⑥ relational Database Rdb
Relational database is a database based on relational model
1. Relational database management System RDBMS
Relational database management system is the computer software of managing relational database
2. Keyword key
Keywords are an important concept in the relational model. It's a logical structure, not a physical part of a database.
Candidate Keyword candidate key if an attribute set can uniquely identify a row of a table without extra attributes, the attribute set is called the Candidate keyword

Primary keyword PRIMARY key
The primary key is a candidate keyword that is singled out as the unique identifier for the row of the table. A table has only one primary key, and the primary key can be called a primary key

Common keywords: Common key
In a relational database, relationships are represented by compatible or identical attributes or groups of attributes. If two relationships have compatible or identical attributes or attribute groups, then this property or group of properties is called the Public keyword of the two relationships

External keyword FOREIGN key
If the public key is the primary key in a relationship, then the public keyword becomes an external keyword for another relationship. This shows that the external keyword represents the relationship between two relationships, with another relationship of the external key to the main table of the table, with the addition of keywords table called the Main table from the table, foreign key to become foreign key