Technical talk about databases

Strictly speaking, a database is a "warehouse that organizes, stores, and manages data according to a data structure." In the daily work of economic management, it is often necessary to put certain relevant data into such a "warehouse" and process it accordingly according to management needs. For example, the personnel department of an enterprise or public institution often stores the basic information of its employees (employee number, name, age, gender, place of origin, salary, resume, etc.) in a table. This table can be regarded as a database . With this "data warehouse", we can query the basic situation of an employee at any time as needed, and we can also query the number of employees whose wages are within a certain range, etc. If all these tasks can be automatically performed on computers, then our personnel management can reach an extremely high level. In addition, many such "databases" also need to be established in financial management, warehouse management, and production management, so that computers can be used to realize automated management of finance, warehouse, and production.

J.Martin gave a relatively complete definition of a database: a database is a collection of related data stored together that is structured, has no harmful or unnecessary redundancy, and provides A variety of application services; data storage is independent of the program that uses it; new data can be inserted into the database, and original data can be modified and retrieved in a common and controllable way. When there are several structurally completely separate databases in a system, the system contains a "database collection".

Definition 2

A database is a collection of data organized according to a certain data model and stored in secondary storage. This kind of data collection has the following characteristics: it is as non-duplicated as possible, serves multiple applications of a specific organization in an optimal way, its data structure is independent of the applications that use it, and the addition, deletion, modification and retrieval of data are performed by Unified software for management and control. From the perspective of development history, database is an advanced stage of data management, which was developed from file management system.

Definition 3 (View of the Expert Committee on the Protocol to the Berne Convention)

All compilations of information (data, facts, etc.), whether in printed form, computer storage unit form, or If it exists in any other form, it should be regarded as a "database".

[Edit this paragraph] The basic structure of the database

The basic structure of the database is divided into three levels, reflecting three different perspectives of observing the database.

(1) Physical data layer.

It is the innermost layer of the database and is a collection of data actually stored on the physical storage device. These data are raw data, which are the objects processed by the user. They are composed of bit strings, characters and words processed by the instruction operations described by the internal mode.

(2) Conceptual data layer.

It is the middle layer of the database and the overall logical representation of the database. It points out the logical definition of each data and the logical connection between data, and is a collection of storage records. It involves the logical relationship of all objects in the database, rather than their physical situation. It is a database under the concept of a database administrator.

(3) Logical data layer.

It is a database that users see and use, and represents a collection of data used by one or some specific users, that is, a collection of logical records.

The connections between different levels of the database are converted through mapping.

[Edit this paragraph] Main features of the database

(1) Realize data sharing.

Data sharing includes that all users can access the data in the database at the same time. It also includes that users can use the database through the interface in various ways and provides data sharing.

(2) Reduce data redundancy.

Compared with the file system, because the database realizes data sharing, it avoids users from creating application files individually. It reduces a large amount of duplicate data, reduces data redundancy, and maintains data consistency.

(3) Data independence.

The independence of data includes that the logical structure of the database in the database and the application are independent of each other, and that changes in the physical structure of the data do not affect the logical structure of the data.

(4) Centralized control of data.

In the file management method, the data is in a scattered state, and there is no relationship between the files of different users or the same user in different processes.

The database can be used to centrally control and manage data, and the data model can be used to represent the organization of various data and the connections between data.

(5) Data consistency and maintainability to ensure data security and reliability.

Mainly include: ① Security control: to prevent data loss, incorrect updates and unauthorized use; ② Integrity control: to ensure the correctness, validity and compatibility of data; ③ Concurrency control: to enable Within the same time period, it allows multiple accesses to data and prevents abnormal interactions between users; ④ Fault discovery and recovery: The database management system provides a set of methods to detect and repair faults in a timely manner. This prevents data from being destroyed