Exercise involves knowledge
15 punch cards today
-
Users use database applications to communicate with the DBMS, access and manage the data stored in the DBMS.
(Although there is already a database management system, but in many cases, the database management system can not meet the user's database management. At this time, you need to use database applications)
-
Data (Data) includes not only the ordinary meaning of the numbers on, also including text, images, sound and so on. In other words, all information used to describe things in a computer can be called data.
-
Database technology is divided into manual management phase, the phase of the file system, database system [stage] .
-
Independence of data comprises logical and physical independence of independence .
-
Please briefly describe the meaning of DB, DBS and DBMS and the relationship between them.
DB : is the abbreviation of Database, which is a warehouse for organizing, storing and managing data according to the data structure.
DBS : is the abbreviation of Database System (DataBase System), refers to the system after the introduction of the database in the computer system.
DBMS : is the abbreviation of Database Management System, a set of software specially used to create and manage databases, which is between applications and operating systems, such as MySQL, Oracle, etc.
The relationship between DB, DBS and DBMS is as follows :
① Multiple DBs can be managed simultaneously in DBMS.
② In addition to databases, DBS also includes DBMS, database applications, etc.
- Database Administrator (DBA)
- The images existing between the outer model and the conceptual model, between the conceptual model and the inner model are secondary images .
- *The inner mode determines how the data is stored in the database.
- External mode can create different views for the needs of different users. And because of the different needs of different users, there are many ways to display data, so there will be multiple external modes in a database, but there is only one conceptual mode and internal mode .
- The Standards Planning And Requirements Committee (SPARC) of the American National Standards Institute (ANSI) proposed the ANSI-SPARC system structure in a research report published in 1971, that is, the three-level model structure ( Or called the three-tier architecture). ANSI-SPARC did not eventually become an official standard , but it is still the basis for understanding database management systems.
- The conceptual model/intra-model mapping reflects physical independence.
Physical independence means that the inner model is modified without affecting the conceptual model and outer model of the upper layer.
For example, if you save an xls file as an xlsx file in Excel, although the file format is changed, the content of the table displayed after the file is opened generally does not change. - [Three-level model] refers to the database management system to manage data from three levels
- Internal mode (also known as physical mode, storage mode) is oriented to the physical database, describing how the data is stored in the disk
- The external mode/conceptual mode image reflects logical independence . Logical independence means that when the conceptual model is modified, it does not affect the outer model of the upper layer.
- Entity refers to things that exist objectively and can be distinguished from each other
- A student can take multiple courses, and a course can be taken by multiple students. There is a many-to-many relationship between students and courses. So the one-to-many relationship between students and courses is wrong.