An overview of database review Database system

Database is the newest technology of data management, and it is 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 the 4 basic concepts closely related to database technology.

Data

Data is the base object stored in the database. There are many kinds of data, such as text, graph, image, audio, video, student's records, transportation of goods and so on. These are part of the data.

There are many different definitions of data, which we can understand as: symbolic records describing things are called data.

The interpretation of data is a description of the meaning of the data, the meaning of the data is called the semantics of data, the data and its semantics are inseparable.

Databases (database, abbreviated DB)

Database, a lot of understanding of the way, is to store data warehouse only. The warehouse is the storage device of the computer, of course, the data is stored in a certain format.

Definition of data:

A database is a collection of large amounts of data that can be shared over a long period of time stored in a computer, organized (with a certain data structure). The data in the database is organized, described and stored according to a certain data model, with small redundancy (redundancy), high data independence and extensibility, and can be shared for various users.

In general, database data has the three most basic features of persistent storage, organization, and sharing.

Database management System (DB Management System,dbms)

Database management system is a layer of database management software which is located between the user and the operating system. The database management system and the operating system are the basic software of the computer as well as a large and complex software system.

The main functions of database management system

1. Data definition function

The----------DBMS provides a data definition language (LANGUAGE,DDL) that allows users to easily define data objects.

2. Data organization, storage and management

The DBMS organizes, stores, and manages various types of data, including data dictionaries, user data, access paths to data, and so on.

The basic goal of data organization and storage is to improve storage space utilization and convenient access, provide multiple access methods (such as index lookup, hash lookup, sequential lookup, etc.) to improve access efficiency.

3. Data manipulation function

The DBMS also provides data manipulation language (manipulation language,dml), which allows users to manipulate data using DML to implement basic operations on the database, such as querying, inserting, deleting, and modifying.

4. Database transaction management and operation management

Database in the establishment, application and maintenance by the database management System Unified management, unified control, in order to ensure the security of data, integrity, multi-user data on the concurrent use and after the failure of the system recovery.

5. Database setup and Maintenance functions

It includes: input of database initial data, transformation function, database dump, recovery function, database organization function and performance monitoring, analysis function and so on. These features are usually replaced by utilities or management tools.

6. Other functions

Including: DBMS and other software systems in the network communication functions, generally by the database, database management system (and its development tools), Application systems, database administrators.

Database technology is due to the need of data management tasks.

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

The processing of data refers to the collection, storage, processing and dissemination of a variety of data, the sum of a series of activities.

3 Stages of software management technology development

First, the artificial management stage

Before the mid 1950s, computers were used primarily for scientific calculations, when the external memory was only tape, card, tape, and no direct access storage devices such as disks. The software situation is no operating system, no management data specialized software, the processing of the data is a batch processing way to deal with. Therefore, the manual management of data has the following characteristics:

1. Data not saved

2. Application Management Data

3. Data not shared

4. Data is not independent

In the manual management phase, the relationship between the program and the data is one by one corresponding.

Ii. Documentation System Phase

In the late the 1950s to the middle of the 60, there were already external memory devices, and in software, there were special data management software in the operating system. Generally referred to as file system, the way of processing in addition to batch processing, and can be implemented online real-time processing.

The characteristics of file system Management data are as follows:

1. Data can be stored for a long time

2. Managing data from the file system

However, there are some shortcomings in the file system, as follows:

1. Large data sharing and redundancy

2. Data independence is poor

3. Concurrent access is prone to exceptions

4. Data security is difficult to control

Third, the database system phase

Features of the database system: (compared to manual management and file systems)

1. Data structuring

The database system realizes the structure of the whole data, which is one of the main characteristics of the database and the essential difference between the database system and the file system.

"Overall" structure refers to the data in the database is no longer only for an application, but for the whole organization, not only the data is structured, and the whole is structured, the data is connected.

2. Data sharing is high, redundancy is low, easy to expand

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

As the data is oriented to the whole system, is structured data, not only can be used by multiple applications sharing, but also easy to add new applications, which makes the database system elastic, easy to expand, can adapt to the needs of users.

3. High data independence

Data independence includes physical independence and logical independence.

Physical independence refers to the fact that the user's application is independent of the data stored in the database on disk. That is, how the data is stored in a database on disk is managed by the DBMS, and the user program does not need to know that the application is only dealing with the logical structure of the data so that the application does not change when the physical storage of the data changes.

Logical independence refers to the user's application and the logical structure of the database is independent of each other. In other words, the logical structure changes, and the user program can not be changed.

4. Data is managed and controlled centrally by the DBMS

The sharing of a database is concurrent (Concurrency) sharing, that is, multiple users can simultaneously store data in the database and even access the same data in the database at the same time.

The DBMS must also provide several data control functions:

4.1. Security protection of data

4.2. Data integrity (Integrity) Check

4.3. Concurrency (Concurrency) control

4.4. Database recovery (Recovery)

An overview of database review Database system