Brief introduction of relational database system

1.1.1 What is relational data
Relational data is data that is represented by a relational mathematical model. The relational mathematical model describes the data in the form of a two-dimensional table, as shown in tables 1.1 and 1.2.

1.1.2 What is a relational database
1. What is the main code (primary key)
A combination of fields or fields that uniquely represents each record in a datasheet is called the primary code.
2. What is the outer code (foreign key)
The Number field in table 1.2 and the Tutor Number field in table 1.1 correspond. The Number field in table 1.2 is the primary code for table 1.2. The "Number" field in Table 1.2 can also be called the Outer Code of Table 1.1.
1.1.3 What is a relational database system
A complete relational database system consists of a 5-tier structure, as shown in Figure 1.1.

1. Hardware
Hardware refers to the computer that installs the database system, including two kinds.
Server
Client
2. Operating system
The operating system refers to the operating system used by the computer where the database system is installed.
3. Relational database management system, database
A relational database is a collection of shareable, organized relational data that is stored on a computer. Relational database management system is a database management software which is located between operating system and relational database application systems.
4. Relational database application System
Relational database application system is a database application software developed by various application development tools (such as VB, Pb and Delphi) and development technology to meet the needs of users.
5. The user
Users refer to people who deal with the database system, including the following 3 categories of personnel.
End user
Database application System Developer
Database administrator
1.1.4 What is a relational database management system
1. Data definition language and translation program DDL
2. Data manipulation Language and compilation (interpretation) program DML
3. Database management procedures