Simple version database review notes [Pi Pilei]
I also recorded the key parts of the book with colors. It's better than looking through the book every time.
To be honest, the database thing has to rely on the question, I have memorized the notes, and the result is still confused when I do the question. The difficulty of the question only knows which one of the notes corresponds to when you choose the answer. . .
Chapter One Introduction
1. Basic concepts:
data ( data ): a symbolic record describing things.
Database ( DB ): a collection of organized and shareable large amounts of data stored in the computer for a long time . The data in the database is organized, described and stored according to a certain data model , with less redundancy , higher data independence and easy scalability , and is shared by various users .
Database Management System ( DBMS ): a layer of data management software located between the user and the operating system. It is
the function of the basic computer software DBMS:
(1) Data definition function (DDL data definition language)
(2) Data organization, storage and management (Data dictionary, user data, etc.)
(3) Data manipulation function (DML data manipulation language)
(4) Database transaction management and operation management (to ensure the safety and integrity of data, concurrent use of data by multiple users and failures After the system recovery)
(5) Database establishment and maintenance function
(6) Other functions (such as: communication function, data conversion function, etc.)
Database system ( DB ): DBS=DB+DBMS+DBA+exe
DBS is composed of DB, A system for storing, managing, processing and maintaining data composed of DBMS (and its application development tools), applications and DBA.
2. Data management technology: (1) Data management is the central issue of data processing
(2)
Manual management stage:
user (programmer)
a certain application has
no sharing, great redundancy and
independence, completely dependent on the program,
no structured
application The program can control itself
File system stage:
File system,
a certain application
, poor sharing, large redundancy, poor
independence,
records have structure, and the overall structure is unstructured. The
application can control itself
Database system stage:
DBMS
real world (one enterprise, one department)
has high sharing, low redundancy,
high physical independence and certain logical independence,
overall structured, described by data model ( data structuring is the phase of database system The essential difference in the file system stage )
DBMS provides data security, integrity, concurrency control and recovery capabilities
3. Features of DBS :
(1) Data structuring (one of the main features, the essential difference between DB and file system)
Details: data in DB is no longer only for a certain application, but for the entire organization or enterprise. Not only the data is internally structured, but the whole is structured, and data is connected.
(2) High data sharing, low redundancy and easy to expand.
Details: Data sharing can greatly reduce data redundancy and save storage space.
Data sharing can avoid incompatibility and inconsistency between data.
Data faces the entire system. It can not only be shared and used by multiple applications, but it is also easy to add new applications. Therefore, DBS is flexible and easy to expand
(3) High data independence.
Physical independence: the user's application and the physical storage of the data in the database are independent of each other.
Logical independence: the user's application and the logical structure of the database are independent of each other
(4) Data is managed and controlled by DBMS:
①Security protection of data: Security refers to the protection of data to prevent data leakage and destruction caused by illegal use
②Integrity protection of data: refers to the correctness, validity and compatibility of data of
③ concurrency control
④ database recovery
4. The database management system performs unified control of the database during the establishment, operation and maintenance of the database to ensure the integrity and security of the data , and performs concurrent control when multiple users use the database at the same time, and restores the database after a failure .
5. DBS makes the information system centered on (program of processing data) -> (around shared database)
6. Data model : The abstraction of real-world data characteristics is the core and foundation of DBS . It is
divided into: conceptual model, logical model, and physical model (not considered in this course)
7. The real world is abstracted into the information world, and then transformed into a machine world
entity : objectively exists any and mutually distinguishable food (a student)
attribute: a certain characteristic of the entity (student number, gender, name)
code : unique Identify the attribute set of the entity (student number is the code of the student entity)
Entity type: Use the entity name and its attribute name set to abstract and describe similar entities (student (student number, name, gender, age))
entity set: (all students) )
Connection: The connection between entities usually refers to the connection between different entity sets ( one-to-one, one-to-many, many-to-many )
8. Entity connection method: E-R method
9. Data model components : data structure, data operation, data integrity constraints
10. Common data models: hierarchical, mesh, relationship (two-dimensional table )
relationship model : Each component must be an indivisible data item
. The data operation in the relational model is a set operation, and the operation object and the operation result are both related
11. The model is relatively stable , while the instance is relatively variable.
12. The model (logical model): a description of the logical structure and characteristics of all data in the database, and a common data view for all users ( 1DB->1 model , Use DDL to define the mode)
External mode (sub-mode/user mode): It is the description of the logical structure and characteristics of the local data that the database user can see and use. The data view mode of the database user is used for the logical representation of data related to a certain application. ( 1DB->Multiple sub-modes )
Internal mode (storage mode): It is the description of the physical structure and storage mode of the data, and the organization mode of the data in the database (1DB->1 internal mode)
13. External mode/mode image : When the mode is changed, the DBA will make corresponding changes to each external mode/mode image to keep the external mode unchanged. The application program is written according to the external mode of the data, so that the application program does not need to be changed, which ensures the logic independence of the data and the program.
Schema/internal schema mapping : When the storage structure of the database changes, the DBA will make corresponding changes to the schema/internal schema mapping, which can keep the schema unchanged, so that the application program remains unchanged, ensuring the physical independence of the data and the program .
14.DBA work:
(1) Determine the information content and structure in the
database (2) Determine the storage structure and access strategy of the database
(3) Define the security requirements and integrity constraints of the data
(4) Monitor the use and Operation
(5) Improvement, reorganization and reconstruction of the database