Database system (DataBase System, referred to as DBS) is a computer hardware and software as a tool, the data is organized into a database format and subjected to storage, management, handling and maintenance of high-performance information processing system.
Part of the database system (five parts)
Computer hardware systems, databases, software systems, database management systems (DBMS), database user.
1. Hardware (Hardware) system
It refers to the hardware store and run the database system. Including CPU, memory, mass storage devices, input / output device and the external equipment.
2. Database (Database)
In the computer, organized, aggregated data can be stored and shared data objects, according to a certain set of this data model or tissue structure, described and long-term storage, and retrieval of data can be performed in a safe and reliable way and storage.
- Integration : the links between the various applications for a particular application environment and the data related to all the data set, and stored according to a certain structure;
- Sharing : The data in the database can be shared by a plurality of different users can simultaneously access the database, or even simultaneously access the same data in the database.
3. Database Users
That is, people who use the database, the database storage, maintenance and retrieval operations.
- The first category of users: the end-user (End User) - non-professional computer, using an application program interface has been prepared using a good database;
- The second category of users: the application programmer - design and preparation and application debugging and installation for the end user;
- The third category of users: database administrator (DBA) - responsible for the design, build, manage and maintain databases, and coordination of user requirements database for personal or work team.
- Database Administrator DBA main responsibilities are as follows:
- Involved in the whole process of database design , determine the structure and content of the entire database;
- Decide database storage structure and access strategy , in order to obtain a high access efficiency and storage space utilization;
- Help application programmers to use database systems , such as training, answer questions encountered daily use database application programmers and other systems;
- Security and integrity of data definition, is responsible for assigning each application access to the database;
- Monitoring the use and operation of the database, the DBA is responsible for defining and implementing the appropriate database backup and recovery strategy ; when the need to change the structure of the database, to complete the modification of the data structure;
- Improvement and remodeling database , space utilization during DBA is responsible for monitoring the operation of the database system, the processing efficiency and other performance indicators.
4. software (Software) System :
Including operating systems, application development tools and database applications systems.
The DBMS (Database Management System, DBMS)
Database System core software . It has the following functions:
① Data definition function : DBMS provides data definition language (DAta Define Language, DDL) schema definition data, the outer and inner pattern mode three mode configuration; custom mode / intra modes, and an outer mode / two image mode; definition of constraints condition.
Defined as a user password and access rights, define integrity rules;
DBMS provides a structured query language (SQL) provides Create, Drop, Alter and other statements may are used to create, delete, and modify the database.
② data manipulation functions : DBMS ** provide data manipulation language (Data Manipulation Language, DML) ** basic operation of the database, including retrieving, updating (including insertion, modification, and deletion) and the like.
DML there are two types: one is autonomous or self-contained type, can be used alone; the other is the host type, embedded in a high-level language need not be used alone.
E.g. DBMS provides a structured query language SQL provide INSERT, DELETE, UPDATE, SELECT operation may be implemented separately in the database to add, delete, search, change the like.
③ run database management functions : the core of the DBMS. DBMS through the control of the database to ensure data is correct, effective and database systems running. Mainly in the following areas:
- Security control : to prevent illegal use of the database and destruction caused by leakage of data, the user can only operate legally privileged data, does not prohibit legitimate user access.
- Integrity control : by providing a number of rules, integrity constraints, to ensure the accuracy, effectiveness, compatibility data.
- Concurrency control : when multiple users simultaneously access or modify the database, the system can be prevented due to the mutual interference provided to the user of the incorrect data, and to prevent damage to the database.
- Data Recovery : incorrect data in the database or data loss, the system has the ability to recover from an error state database to the correct state recently at a certain time.
The establishment and maintenance functions ④ database: completed by each utility DBMS related functions:
- A database establishing includes initial data loading and data conversion database, and the like;
- Database maintenance , including a database dump, restore, re-organize and re-structure, system performance monitoring and analysis.
⑤ data organization, storage and management : DBMS is responsible for the organization, storage and management of all kinds of data to be stored, the file structure to determine in what way and access the physical organization of these data to improve storage space utilization and database additions or deletions to change search efficiency.
⑥ data communication interface : DBMS provides a function to communicate with other software.
