Introduction to basic database technology knowledge (1)

DatabaseTechnologyBasic knowledgeIntroduction: Many database beginners have little or no knowledge about database technology. My article will guide you to the most basic level of the database, this allows you to have a better understanding of the basic knowledge of database technology, so as to better master the basic knowledge of database technology and apply the database technology to your daily work and life, which will be very convenient. The following describes the basic knowledge of database technology.

Database technology is a comprehensive software technology and an essential knowledge for using computers for various information management.

Database technology is a new discipline of information management automation that emerged in the 1960s S. It is an important branch of computer science. With the continuous development of computer applications, data processing becomes more and more dominant in the computer application field, and database technology is also widely used.

I. Historical Development of databases

Databases are the product of data management. Data management is the core task of a database, including data classification, organization, encoding, storage, retrieval, and maintenance. With the development of computer hardware and software, database technology continues to develop. From the perspective of data management, the database technology has gone through the manual management, file system, and database system stages.

1. manual management stage

The artificial management stage refers to the early days of the birth of computers (before the late 1950s s). Computers in this period are mainly used for scientific computing. From the perspective of hardware, there are no storage devices for direct access such as disks; from the perspective of software, there is no operating system or software for data management, and the data processing method is batch processing.

In this period, data management features:

1). Data is not saved

Computers in this period are mainly used in scientific computing. Generally, data does not need to be stored for a long time, but data is input during computing of a certain subject, and raw data is not saved after use, the calculation results are not saved.

2). No software system for data management

Programmers must not only define the logical structure of data, but also design physical structures in the program, including storage structures, access methods, and input/output methods. Therefore, the subroutine used to access data in the program changes with the storage changes, and the data is not consistent with the program.

3). No file Concept

Data must be organized by programmers themselves.

4). A group of data corresponds to a program, and the data is application-oriented.

Even if the two programs use the same data, they must define and organize the data separately. The data cannot be shared, used, and referenced, resulting in a large amount of repeated data between the program and the program.

2. File System Phase

The file system stage refers to the stage in which computers are used not only for scientific computing, but also for data management in large quantities (from the late 1950s s to the mid 1960s S ). In terms of hardware, external storage has disks, drums, and other storage devices for direct access. In terms of software, the operating system already has software specifically used for data management, called a file system.

In this period, data management features:

1) data needs to be stored on external storage for reuse for a long time

Because a large number of computers are used for data processing, and files are often queried, modified, inserted, and deleted, data needs to be retained for a long time for repeated operations.

2). There is a certain degree of independence between programs.

The operating system provides the file management function and the method for accessing files. The program and data have an interface for data access. The program can deal with data through file names, there is no need to look for the physical storage location of the Data. At this point, the data has the difference between the physical structure and the logical structure, but the independence between the program and the data is still insufficient.

3). diverse file formats

Because you already have a storage device for direct access, files are no longer limited to sequential files, as well as index files and linked list files. Therefore, access to files can be sequential, or direct access.

4) data is stored in records.

It can be seen that the data and programs in the file system are independent, but they are not yet adequate. Each file still corresponds to an application, and the data is application-oriented. It is very difficult to add new applications to existing data, and the system is not easy to expand. Once the logical structure of the data changes, the application must be modified. In addition, files are isolated and cannot reflect the internal relationships between real-world things. Different applications cannot share the same data, resulting in high data redundancy, inconsistency of the same data is easy to generate.

3. Database System stage

The database system stage began in the late 1960s S. In this phase, the data in the database is no longer oriented to an application or a program, but to the entire enterprise (organization) or application.

The database system stage has the following features:

1). Use a complex structured data model

The database system must not only describe the data, but also the relationship between the data. This connection is achieved through the access path.

2). High Data independence

Data and programs are independent of each other. Changes in the data storage structure do not affect the use of user programs.

3). Lowest Redundancy

Duplicate data in the database system is minimized so that more data can be stored in a limited storage space and access time can be reduced.

4). Data Control

The database system has data security to prevent data loss and unauthorized use. It has data integrity to ensure data correctness, effectiveness, and compatibility. It has concurrent data control, avoid mutual interference between concurrent programs. With the data recovery function, the system has the ability to restore the database to the correct state at a recent time when the database is damaged or the data is unreliable.

To sum up, a database can be defined as a collection of data that is stored and associated with each other. It is shared with multiple users and has minimum redundancy and high data independence.

4. Development of three generations of Database Systems

The data model is the core of the database system. According to the main line of data model development, the formation process and development of database technology can be reflected in the following three aspects:

1). First-generation database system-hierarchical and mesh Database Management System

Representative Products of hierarchical and mesh databases are the hierarchical model database management system developed by IBM in 1969. Hierarchical databases are the pioneers of database systems, while network databases are the foundation of database concepts, methods, and technologies.

2). Second-generation database system-Relational Database Management System (RDBMS)

In 1970, an IBM researcher E. f. in the paper titled "relational model of large shared database data", Codd puts forward the relational model of the database, which lays a theoretical foundation for the relational database technology. By 1980s, almost all newly developed database systems were relational.

James Gray is the key person who makes the relational database technology practical. Gray plays a key role in solving major technical issues such as how to ensure data integrity, security, concurrency, and database fault recovery capabilities.

The emergence of relational database systems has promoted the miniaturization and popularization of databases, making it possible to configure database systems on micro machines.