Introduction to Database Systems
introduction
Chapter One Introduction
- 1.1 Overview of the database system
- 1.2 Data Model
- 1.3 Structure of the database system
- 1.4 Composition of the database system
- 1.5 Summary
1. Four basic concepts in the database system
- data
- database
- database management system
- Database systems
1. Data
Data is the basic object stored in the database
data definition
Symbolic records describing things
type of data
Numbers, text, graphics, images, audio, video, student records, order status, etc.
The meaning of data is called the semantics of data, and data and its semantics are inseparable.
For example, 93 is a data
- Semantic 1: A student's grade in a certain course
- Semantic 2: Someone's weight
- Semantic 3: The number of students in the computer department in 2014
- Semantic 4: Ask students to give...
2. Database
3. Database management system
What is a Database Management System (DBMS)
- A layer of data management software that sits between user applications and the operating system
- It is basic software, a large and complex software system
Uses of database management systems
Organize and store data scientifically, acquire and maintain data efficiently
The main functions of the database management system
1. Data definition function
- Provides Data Definition Language (DDL)
- Define data objects in the database
2. Data organization, storage and management
- Classify, organize, store and manage various data
- Determine how data is structured and accessed at the storage level
- Realize the connection between data
- Provide multiple access methods to improve access efficiency
3. Data manipulation function
- Provides Data Manipulation Language (DML)
- Implement basic operations on the database (query, insert, delete, and modify)
4. Database transaction management and operation management
- Data security, integrity, concurrent use of data by multiple users
- System recovery database after failure
- It is uniformly managed and controlled by the database management system to ensure the correct operation of the transaction.
5. Database establishment and maintenance functions
- Provide utilities/tools to complete database data bulk loading, database dump, media failure recovery, database reorganization and performance monitoring, etc.
6. Other functions
- Communication between the database management system and other software systems in the network
- Data conversion between database management systems
- Mutual access and interoperability between heterogeneous databases
4. Database system
2. The emergence and development of data management technology
What is data management
- Classify, organize, encode, store, retrieve and maintain data
- Central issues in data processing and data analysis
The development process of data management technology
- Manual management stage (before mid-1950s)
- File system stage (late 1950s-mid 1960s)
- Database system stage (late 1960s - present)
Comparison of the three phases of data management
Three, the characteristics of the database system
- data structuring
- High data sharing, low redundancy and easy expansion
- High data independence
- The data is uniformly managed and controlled by the database management system
data structuring
High data independence
- Physical independence
means that the user's application program and the physical storage of data in the database are independent of each other. When the physical storage of data changes, the application does not change. - Logical independence
means that the logical structure of the application program and the database accessed by the user is independent of each other. The logical structure of the data has changed, and the application program does not need to be changed.
Data independence is guaranteed by the secondary image function of the database management system.
The data is uniformly managed and controlled by the database management system
database definition
- A database is a large collection of data organized and shared in a computer for a long period of time.
- It can be shared by various users with minimum redundancy and high data independence.
- The database management system performs unified control on the database during the establishment, operation and maintenance of the database to ensure the integrity and security of the data, and performs concurrency control when multiple users use it at the same time, and restores the database after a failure occurs.