Database Management System
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Database Management System |
Database management system (Database Management System, DBMS) is a large-scale software for manipulating and managing databases, and is used to establish, use and maintain databases. It manages and controls the database uniformly to ensure the security and integrity of the database.
Users access data in the database through dbms, and database administrators also perform database maintenance through dbms. It provides a variety of functions, enabling multiple applications and users to use different methods to create, modify and query the database at the same time or at different times. It enables users to easily define and manipulate data, maintain data security and integrity, and perform concurrent control and database recovery under multiple users.
The earliest use of "database" as a phrase was in June 1963, when SystemDevelopmentCorporation sponsored a seminar entitled "DevelopmentandManagementofaComputer-centeredDataBase". Database appeared in large numbers in Europe in the early 1970s as an independent word, and was not used by major American newspapers until the end of the twentieth century.
Database Management System Components
According to the function, the database management system can be roughly divided into 6 parts:
(1) Schema translation: Provide data definition language (ddl). Database schemas written in it are translated into internal representations. The logical structure, integrity constraints and physical storage structure of the database are stored in the internal data dictionary. Various data operations of the database (such as searching, modifying, inserting and deleting, etc.) and the maintenance and management of the database are all based on the database schema.
(2) Compilation of the application program: Compile the application program containing the statement of accessing the database into a target program that can be run under the support of dbms.
(3) Interactive query: provide an easy-to-use interactive query language, such as sql. dbms is responsible for executing query commands and displaying the query results on the screen.
(4) Organization and access of data: Provide physical organization and access methods of data on peripheral storage devices.
(5) Transaction operation management: Provide transaction operation management and operation log, transaction operation security monitoring and data integrity check, transaction concurrency control and system recovery and other functions.
(6) Database maintenance: Provide software support for database administrators, including maintenance tools such as data security control, integrity assurance, database backup, database reorganization, and performance monitoring.
The database management system based on the relational model has been perfected day by day, and has been widely used in all walks of life as commercial software. Its application in the distributed multi-user environment of each household server structure further expands the application of the database system. With the advancement of new data model and data management implementation technology, it can be expected that the performance of dbms software will be updated and improved, and the application field will be further expanded.
The functions it provides are the following:
(1) Data definition function. DBMS provides the corresponding data language to define (DDL) database structure, they are the description of the database framework, and are stored in the data dictionary.
(2) Data access function. DBMS provides Data Manipulation Language (DML) to implement basic access operations on database data: retrieval, insertion, modification and deletion.
(3) Database operation and management functions. DBMS provides data control functions, that is, data security, integrity and concurrency control to effectively control and manage database operations to ensure that data is correct and effective.
(4) The establishment and maintenance of the database. Including the loading of database initial data, database dumping, recovery, reorganization, system performance monitoring, analysis and other functions.
(5) The transmission of the database. The DBMS provides the transmission of processing data and realizes the communication between the user program and the DBMS, usually in coordination with the operating system.
The Hierarchy of Database Management Systems
According to the different processing objects, the hierarchical structure of the database management system from high to low is the application layer, the language translation processing layer, the data access layer, the data storage layer, and the operating system.
(1) Application layer. The application layer is the interface layer between the DBMS and end users and application programs, and the objects processed are various database applications.
(2) Language translation processing layer. The language translation processing layer is to perform syntax analysis, view conversion, authorization check, integrity check, etc. on various statements in the database language.
(3) Data access layer. The object handled by the data access layer is a single tuple, which converts the upper-level set operations into single-record operations.
(4) Data storage layer. The objects handled by the data storage layer are data pages and system buffers.
(5) Operating system. The operating system is the foundation of the DBMS. The access primitives and basic access methods provided by the operating system are usually used as interfaces with the DBMS storage layer.
Database History
The first database management system was developed in 1960. The pioneer in this field was Charles Bachman.
Bachman's early documented purpose was to make more efficient use of new direct-access storage devices: prior to this, data processing was based on punched cards and magnetic tape, and the series of actions were primarily processing activities.
Two major data models have continued since then: the network model developed by CODASYL based on ideas from Bachman, and the (apparently independent) hierarchical model applied in a system developed by North American Rockwell and later used by IBM as the basis for their IMS products.
The relational model was proposed by E.F. Codd in 1970. He criticized the model structure of the time for confusing the abstract description of the information structure and the description of the material access mechanism.
For a long time, relational models remained of only academic interest. At the same time, the CODASYL system and IMS were regarded as practical engineering solutions, and the relational model adopted at that time was more at the stage of theoretical viewpoints, and it was (correctly) advocated that software and hardware technologies should be followed up in time.
The first implementations are Michael Stonebraker's Ingres at Berkeley University and IBM's SystemR project. Both are research circles, published in 1976. The first commercial products, Oracle and DB2, appeared around 1980. The first successful microcomputer database product was dBASE running on CP/M and PC-DOS/MS-DOS operating systems. In the 1980s, research activity focused on distributed database systems and database machines, but these advances had little impact on the market.
Another important theoretical idea is the functional data model, but it has received little global attention except for specialized applications such as genetics, molecular biology, fraud investigation, etc.
In the 90s, the focus shifted to object-oriented databases. There has been some success in areas that need to handle more complex data than relational databases, such as spatial databases, data engineering (including software engineering libraries), and multimedia data. Some ideas have been adopted by relational database vendors, integrating chneg as a new feature in the product.
In the 2000s, a popular area of innovation was XML databases. Along with relational databases, many new GEM companies have emerged, but at the same time important ideas have been incorporated into existing relational database products.
The goal of XML databases is to eliminate the separation of documents and data in traditional databases, allowing an organization's information resources to be stored in the same place, regardless of whether they are highly systematic resources.
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