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Database is the latest technology of data management and an important branch of computer science. From online transaction processing (On-Line Transaction Processing,OLTP) to online Feixi processing (On-Line Analysis Processing,OLAP), from general enterprise management to computer aided design and manufacturing (CAD/CAM), computer integrated manufacturing system (CIMS), e-government (e-Convernment), e-commerce (e-Commerce) geographic information system (GIS) and so on.

Data, database, database management system and database system are four basic concepts closely related to database technology.

data

Data is the basic object stored in the database. There are many kinds of data, such as text (Text), graphics (graph), image (Image), audio (Audio), video (Video), student records, transportation of goods, and so on. These are all parts of the data.

The definition of data varies, and we can uniformly understand that the symbolic record that describes things is called data.

The interpretation of data refers to the explanation of the meaning of data, the meaning of data is called the semantics of data, and data and its semantics are inseparable.

Database (Database, DB for short)

A database, a lot of ways to understand it, is just a warehouse for storing data. The warehouse is the storage device of the computer, of course, the data is also stored in a certain format.

Definition of data:

A database is a collection of large amounts of data that are long-term stored in a computer, organized (with a certain data structure) and can be shared. The data in the database is organized, described and stored according to a certain data model, with less redundancy (redundancy), high data independence (data independence) and easy expansibility, and can be shared by all kinds of users.

Generally speaking, database data has the three most basic characteristics of permanent storage, organization and sharability.

Database management system (Database Management System,DBMS)

Database management system is a layer of database management software located between the user and the operating system. Like the operating system, database management system is not only the basic software of computer, but also a large and complex software system.

Main functions of database management system

1. Data definition function

-DBMS provides data definition language (Data Definition Language,DDL), through which users can easily define data objects.

two。 Data organization, storage and management

DBMS classifies, organizes, stores and manages all kinds of data, including data dictionaries, user data, access paths of data, etc.

The basic goal of data organization and storage is to improve storage space utilization and facilitate access, and provide a variety of access methods (such as index lookup, Hash lookup, sequential lookup, etc.) to improve access efficiency.

3. Data operation function

DBMS also provides data manipulation language (data Manipulation Language,DML). Users can use DML to manipulate data and achieve basic operations on the database, such as query, insertion, deletion and modification.

4. Transaction Management and Operation Management of Database

The database is uniformly managed and controlled by the database management system during the establishment, application and maintenance of the database, so as to ensure the security and integrity of the data, the concurrent use of data by multiple users and the recovery of the system after failure.

5. Establishment and maintenance function of database

It includes: the input and conversion function of the initial data of the database, the dump and recovery function of the database, the reorganization function and the performance monitoring and analysis function of the database. These functions are usually replaced by utilities or management tools.

6. Other functions

It includes: the communication function between DBMS and other software systems in the network, which is generally composed of database, database management system (and its development tools), application system and database administrator.

Database technology is produced in response to the needs of data management tasks.

Data management refers to the analysis, organization, coding, storage, retrieval and maintenance of data, which is the central issue of data processing.

Data processing refers to the sum of a series of activities for collecting, storing, processing and disseminating all kinds of data.

Three stages of the Development of Software Management Technology

I. the stage of manual management

Before the mid-1950s, computers were mainly used for scientific computing, when the external memory was only paper tape, cards, magnetic tapes, no disks and other direct access storage devices. The software has no operating system, no special software for managing data, and batch processing is used for data processing. Therefore, manual management data has the following characteristics:

1. Data is not saved

two。 Application management data

3. Data is not shared

4. The data is not independent

In the stage of manual management, the relationship between programs and data is one-to-one.

II. File system phase

From the late 1950s to the mid-1960s, external storage devices already existed; in terms of software, there was also special data management software in the operating system. Generally known as the file system, the way of processing in addition to batch processing, and can achieve on-line real-time processing.

The characteristics of file system management data are as follows:

1. Data can be preserved for a long time.

two。 Data is managed by the file system

However, the file system has some shortcomings, as follows:

1. Large data sharing and redundancy

two。 The independence of data is poor.

3. Concurrent access is easy to produce exceptions

4. The security of data is difficult to control.

III. Database system stage

Characteristics of database system: (compared with manual management and file system)

1. Data structure

The database system realizes the structure of the overall data, which is not only one of the main features of the database, but also the essential difference between the database system and the file system.

"holistic" structuralization means that the data in the database is no longer only for a certain application, but for the whole organization; not only the data is structured internally, but also the whole is structured, and there are connections between the data.

two。 The data has high sharing, low redundancy and easy expansion.

Data sharing can greatly reduce data redundancy and save storage space, and data sharing can also avoid incompatibility and inconsistency between data.

Because the data is oriented to the whole system and is structured data, it can not only be shared by multiple applications, but also easy to add new applications, which makes the database system flexible, easy to expand, and can adapt to the various needs of users.

3. High data independence

Data independence includes physical independence and logical independence.

Physical independence means that the user's application is independent of the data stored in the database on disk. In other words, how the data is stored in the database on disk is managed by DBMS, the user program does not need to understand, and the application only deals with the logical structure of the data, so that when the physical storage of the data changes, the application does not have to change.

Logical independence means that the logical structure of the user's application and database are independent of each other. That is to say, the logical structure has changed, and the user program can not be changed.

4. Data is uniformly managed and controlled by DBMS

Database sharing is Concurrency, that is, multiple users can store data in the database or even access the same data in the database at the same time.

DBMS must also provide several data control functions:

4.1. data security (Security) protection

4.2.Integrity of data (Integrity) check

4.3.concurrency (Concurrency) control

4.4.Database recovery (Recovery)

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