Introduction to Database Systems

Chapter 1 Introduction to Database Systems
Introduction
In computer applications, data processing accounts for about 70%. database Technology focuses on how to store, use, and manage data, which is the latest development phase of computer data management technology. databases store a universal set of related data, including not only the data itself, but also the relationship between the data.
1.1.1 data, information and data processing
1. Concepts of data
Data refers to the symbolic data stored in a media set that can be identified.
2. concepts of information
Information is a comprehensive reflection of the existence or movement patterns of things in the real world. It is the knowledge people need to carry out various activities.
3. Data Processing
Refers to the process of converting data into information.
4. Relationship between data information
1.1 data and information
Data is the physical symbol of the load information. Information is the data that people digest and understand, and the understanding of the objective world.
Data is raw materials, input, output, and output.
1.1.2 Information System
1. Information System
A Computer Information System is a unified whole composed of personnel, devices, programs, and data sets for specific purposes.
2. Manage Information System categories
1.1 data and information
Data Processing System
Management Information System (MIS)
Decision Support System
Computer Data Management has gone through the following four
Advanced Development Process:
Manual management stage
File System Phase
Database System stage
Distributed Database System stage
1.2 Development of Computer Data Management
1.2.1 manual management stage
1. Features of data management in the manual management phase:
Data and programs are not independent
Data is not stored for a long time
No software for data management in the system
1.2 Development of Computer Data Management
1.2.2 file system Stage
1. Features
Programs and data have a certain degree of independence. programs and data are stored separately. There is a difference between program files and data files. with the support of the file system, there may be some differences between the logical and physical structures of data, and there is physical independence between the data and the program. The program only needs to access the data using the file name, do not worry about the physical location of the data.
2. logical and physical structures of data
Logical Structure refers to the data structure presented to the user
Physical structure refers to the actual storage structure of data on physical devices.
3. File System Problems
Large data redundancy
Lack of data independence
No centralized data management
1.2 Development of Computer Data Management
1.2.3 database system Stage
1. Basic Concepts
A database is a universal collection of related data. It includes not only the data itself, but also the relationship between the relevant data.
Database Management System (DBMS) refers to the software configured for database creation, use, and maintenance.
2. Database System features
Data sharing to reduce data redundancy
Use a specific data model to reflect the relationship between data
High Data independence
Unified Data control functions (concurrency control, security control, and data integrity control)
1.2 Development of Computer Data Management
1.2.4 distributed database system Stage
1. distributed database systems are the product of the combination of database technology and network technology. distributed databases are logically unified and geographically distributed data sets.
2. distributed database features
Distribution transparency
Combination of local autonomy and centralized control
Reliability and availability
Efficiency and flexibility
1.2 Development of Computer Data Management
1.3.1 composition of Database Systems
A database system is a computer system after the database technology is introduced, including:
Hardware System
Database set
System Software
DBMS: Software configured for database creation, use, and maintenance
Operating System
Other System Software
Database Administrator
User
1.3 Database System
1.3.2 main functions of DBMS
1. Three-Level Architecture of DBMS two-level independence
Level 3 Structure
Local logical structure of data, overall logical structure, physical storage structure
Two levels of independence
Physical independence of data: When the storage structure of data changes, the system provides an image or conversion function between the physical structure and the logical structure of the data to keep the logical structure of the data unchanged, therefore, the application does not need to be modified.
Logical independence of data: the system provides an image or conversion function between the overall logical structure of data and the local logical structure for a specific application. When the overall logical structure of data changes, the local logical structure remains unchanged through the image, so that the application does not need to be modified.
1.3 Database System
1.3.2. Main Functions of DBMS
2. Main Functions of DBMS
Database definition function
Data manipulation
Database Operation Control
Data Integrity Control
Data concurrency control
Data Security Control
Database Restoration
Data Dictionary
1.3 Database System
1.4.1 Data Integrity Control
1. Domain Integrity Control
That is, the field definition field control, the input data must be within the definition Field
2. Association Integrity Control
There may be a certain internal logical relationship between the data in the database. When modifying such data, you must refer to the data related to it or modify it at the same time.
1.4 database protection
1.4.2 Concurrency Control
A prominent advantage of the database system is data sharing. In a shared environment, when multiple users simultaneously access a database, concurrency control must be implemented.
1.4 database protection
1.4.3 Data Security Control
1. user identification and Identification
2. Access Authorization
3. Data Encryption
4. Ensure environment security
1.4 database protection
1.4.4 database recovery
1. "inverted database"-periodic transfer to the entire database
2. Create a log file
3. In the event of a fault, the database is restored to the latest correct status based on database times and log files.
1.4 database protection
1.5.1 trigger
1. Real World
2. concept world
Entity
Attribute-describes the characteristics of an object
Keyword: uniquely identifies the attribute or Attribute combination of each object in an object set. You can select a keyword.
Contact- ing between entities
3. machine world
1.5 Data Model
1.5.2 contact types between entities
1. One-to-one connection)
2. One-to-multiple connections (1: N)
3. Multi-to-Multi-contact (M: N)
1.5 Data Model
Course Selection for subordinate School Students
1 1 1 m n
1.5.3 basic data model type
1. Hierarchical Data Model
2. Mesh Model
3. Link Model
1.5 Data Model