A: The database system DBS (Data Base System) contains the database DB (Data Base) and database management systems DBMS (Database Management System).
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A database system
concept
Is a database system to meet the needs of data processing and developed an ideal data processing system, it is also a real run for the storage, maintenance software system providing data and application systems, storage media, handling objects and management systems the aggregates.
Database system must meet the following requirements:
① to ensure the independence of the data. Independent data and programs will help speed up software development time, save development costs.
② less redundant data, the high degree of data sharing.
③ system's user interface is simple, user-friendly, easy to use.
④ to ensure that the system is reliable and can quickly rule out a fault; to protect data from unauthorized access or who destroy; to prevent error data, once generated can discover.
⑤ have the ability to re-organization of data, or data storage structure change data storage locations, to accommodate changes in the operating characteristics of the user, due to frequent insertion improvement, data organization and messy temporal performance deterioration caused by the deletion condition.
⑥ with modifiable and scalability.
⑦ can adequately describe the intrinsic link between data.
Common database systems:
MySQL
MySQL is a fast, multi-threaded, multi-user and robust SQL database server. MySQL server to support mission-critical, heavy load using the production system, you can also embed it in a large configuration (mass- deployed) software to go.
SQL Server
SQL Server provides a number of Web and e-commerce features, such as rich support for XML and Internet standards, for easy secure access to data via Web, a powerful, flexible, and secure Web-based application management.
Oracle
Oracle product line, including almost all applications, large-scale, complete, safe, and can support multiple instances running at the same time, strong function. It can run on all major platforms. Fully supports all industry standards. A completely open policy. It allows customers to choose the most appropriate solution. Full support for developers.
Second, the database management system
DBMS (Database Management System) is a large-scale software for manipulating and managing a database, used to create, use and maintenance of the database, referred to as DBMS. It unified database management and control, in order to ensure the security and integrity of the database. Users, database administrators perform database maintenance by dbms DBMS data by accessing the database. It allows multiple applications and users in different ways to different times or at the same time to establish, modify and query a database. Most DBMS provides data definition language DDL (Data Definition Language) and data manipulation language DML (Data Manipulation Language), the structure and mode permissions for user-defined database constraints, to achieve the additional data, delete files.
The main function:
1. Data Definition: DBMS provides data definition language DDL (Data Definition Language), three user-defined mode for database structure, and two image integrity constraints and constraints such as confidentiality restrictions. DDL is mainly used to establish, modify the database structure of the database. DDL database structure described merely provides a framework for a database, the database information frame is stored in the data dictionary (Data Dictionary) in.
2. Data Manipulation: DBMS provides data manipulation language DML (Data Manipulation Language), for users to realize additional data, delete, update, query and other operations.
3. Run the database management: operation and management functions of DBMS database is operational control, management, organization and management concurrency control in multi-user environments, security checks and access control restrictions, and perform integrity checks, run logs , management services and automatic recovery, which is to ensure transaction atomicity. These features ensure the normal operation of the database system.
4. The data organization, storage and management: DBMS to organize the classification, storage and management of various kinds of data, including data dictionary, user data, access paths, etc., to be determined in what manner the file structure and organization of such access on the storage level data, how to realize the link between the data. The basic target data storage and organization is to improve utilization of storage space, to select the appropriate access method to improve access efficiency.
5. protection of databases: data in the database is a strategic resource of the information society, it is essential to protect data. DBMS implemented by four aspects of the protection of databases: Restore the database, the database concurrency control, integrity control database, database security control. Other protection features include DBMS buffer management system and data storage of some adaptive mechanism.
6. Database Maintenance: This section includes loading data from the database, the conversion, dump, reassembly and reconstruction database performance monitoring and other functions, these functions are accomplished by the use of each program.
The communication: DBMS processing line having an operating system, time-sharing system and remote job entry associated interfaces for processing of transmission data. The database system in a network environment, should further comprising interoperation between the DBMS and the network communication function of other software and database systems.
Common database:
Dream up a database
SYBASE
DB2
ORACLE
MySQL
ACCESS
Visual Foxpro
MS SQL Server
Informix
PostgreSQL
Third, database
Database (Database) is in accordance with the data structure to organize, store and manage data warehouses, which produces younger than sixty years ago, with the development of information technology and the market, especially after the 1990s, data management not just data storage and management, and converted into various data required for a user managed. There are many types of databases, from the simplest form various data stores to be able to carry out mass data storage of large database systems have been widely used in various aspects.
Database features:
⑴ data sharing
It contains all the user data sharing access to data in the database, but also can include a user interface in various ways by the database, and provide data sharing.
⑵ reduce data redundancy
Compared with the file system, because the database to achieve the data sharing, thus avoiding the user build their own application files. It reduces the amount of duplicate data, reduce data redundancy, maintain data consistency.
⑶ data of independence
Independence of the data includes a logical independence (logical structure of the database and the application database independent) and physical independence (change data does not affect the physical structure of the logical structure data).
⑷ data centralized control
Document management, the data are in a dispersed state, the same user or different users in different treatments between unrelated files. Use database data can be centralized control and management, and that the link between the various data organization and data through the data model.
⑸ data consistency and maintainability to ensure the safety and reliability of the data
Include: ① security control: to prevent data loss, unauthorized use and update error; ② integrity control: to ensure accuracy, effectiveness and compatibility of data; ③ concurrency control: in the same time period, allowing data achieve multiple access, but also to prevent the abnormal interaction between users.
⑹ Recovery
The method provided by the set of database management system, to detect faults and fault repair, thereby preventing data corruption. The database system can recover as soon as possible failure of the database system is running, it may be wrong physically or logically. Such as misuse of the system due to data errors.
Database Type:
Database is usually divided into hierarchical database, network database and relational database three. The database is different according to different data structures and organizations to contact.