Overview of database system

Introduction to database system

One 、 Four basic concepts of database

data ： The symbolic record that describes things is called data . for example ： Text , graphics , video , Audio, etc. are all data .

The meaning of data is called data semantics , Data and its semantics are inseparable .

database ： Databases are stored in computers for a long time 、 organized 、 A collection of large amounts of data that can be shared . The data in the database is organized according to a certain data model , Describe and store , There is less redundancy , High data independence and scalability , And can be shared for a variety of users .
In a nutshell ： The database has permanent storage 、 Organized 、 Three basic features can be shared

Database management system ： It is a layer of data management software between the user and the operating system , Like the operating system, it is the basic software of the computer .

The main function ：

			   Data definition function 
		 	   Data organization 、 Storage and management 
			   Data manipulation function 
			   Database transaction management and operation management 
			   Establishment and maintenance of database 
			   Other features 

Database system ： The database system consists of a database 、 Database management system （ And its application development tools ）、 Storage composed of application and database administrators 、 management 、 A system that processes and maintains data .

Two 、 Characteristics of database system

1. Data structure

The database system realizes the structure of the whole data , This is the main feature of database .

2. High data sharing , Low redundancy and easy expansion

Due to the sharing of data, the redundancy of data is greatly reduced , It saves storage space and avoids incompatibility and inconsistency between data . The database system is flexible , Easy to expand .

3. High data independence

Data independence includes physical independence and logical independence .

• Physical independence ： The user's application and the physical storage of data in the database are independent of each other . So that the user program does not need to manage how the data is stored in the database , When the physical storage of data changes, the user program does not need to change .
• Logical independence ： The logical structure of the user's application and database is independent of each other . That is, when the logical structure of the database changes, the user program does not need to change .

4. Data is managed and controlled by database management system

• Data security protection ： Protection data , Prevent data leakage and damage caused by illegal use
• Data integrity protection ： The correctness of the data 、 Effectiveness and compatibility
• concurrency control ： Control and coordinate the concurrent operations of multiple users
• Database recovery ： Restore the database from the wrong state to a known correct state

3、 ... and 、 summary

Databases make long-term storage organized in computers 、 A lot of 、 Shared data collection . It can be shared by various users , It has minimum redundancy and high data independence . The database management system is established in the database 、 Unified control of database during operation and maintenance , To ensure data integrity and security , And concurrency control when multiple users use the database at the same time , Recover the database after failure .