Review of database -- 1. Overview

                                                                                              summary

1. Stage ： Manual management — file system — database
2. Data model ： Represents an entity type Between and entities Relationship Model of , It is generally used to describe the structure of data in a database

               Three elements ： data structure , Data manipulation , Data constraints

                     classification ：（1） Conceptual data model ： Abstract data model from the information world

                                （2）( structure ) Data model ： Abstracted from the computer world DBMS Supported data models

    3. Conceptual data model ： use   Entity - How to contact （E-R chart ） Express

    4. Structural data model ： Design computer system and database management system （ level （ Trees , one-on-one ）, Reticular （ chart , one-on-one , One to many , Many to many ）, Relationship （ Two dimensional tables , one-on-one , One to many , Many to many ）, object-oriented ( class hierarchy ) Wait for the model ）

              The term ： file ----n A record ----n Data items （ Field ）

    5. Database architecture （ Three level structure ）

                External model ： Partial logical view

                conceptual model ： Global logical view

                Inner model ： data Physical storage model

  6. Database system （DBS） Including hardware , database （DB）, Database management system （DBMS）, And software , All kinds of personnel （ Database administrator DBA, Other personnel, etc ）

7.DBMS The main function of ： Data definition （ Provide DDL Data definition language ）, Data manipulation （ Provide DML Data manipulation language ）, The management and operation of the database , The establishment and maintenance of database

8.DML It can be used in two ways ：（1） Self contained language -- Data query , Data update     （2） Host language -- Embedded in high level language

9.DBMS It manages structured data , It is located in User and operating system Between a layer of data management software

10. The essential difference between the files in the database system and the files in the file system is ：

Kiss security in file system is application-oriented , Basically corresponds to an application , There is no connection between files , Large data redundancy , Poor sharing , Data independent difference ;

Files in the database system are the opposite , Documents are interrelated , Reduced data redundancy , Realize the sharing of data , The independence of data is high

11. Three models ：（ Outside ） Subscheme （ User database ）, Pattern （ Conceptual database ）, Internal mode （ Physical database ）, Be careful ： Sub patterns can be composed of multiple , There can only be one mode and inner mode , Outer patterns are subsets of patterns

12. The independence of data is determined by DBMS Second level image of , Database system usually adopts external mode , Pattern , Three level structure of internal mode ,DBMS It is to use this three-level structure to provide external mode / Mode and mode / Inner mode two-tier image

13. A data dictionary is a collection of description and control information in a database system , It is a powerful tool for database design and management , Yes “ The database of the database ” Known as the