Basic knowledge summary of database

1. Databases are stored in computers for a long time , An organized and sharable collection of large amounts of data . The data in the database is organized according to a certain data model Description and storage , With less redundancy , High data independence and scalability , And can be shared for a variety of users .
2. The database system consists of a database data management system ( And its application development tools ) Storage composed of application and database administrators management A system that processes and maintains data .
3. The independence of data crying is high : Data independence Physical independence Logical independence .
4. The data is uniformly managed and controlled by the database management system : Data security protection Expression of data integrity concurrency control Database recovery .
5. Data models are usually composed of data structures Data manipulation Data integrity constraints .
6. The representation of conceptual model : Entity – contact .
7. The data structure of the relational model : Relationship : A relationship usually corresponds to a table . Tuples : A row in the table is a tuple attribute : A column is an attribute code : It's only certain ( Such as determining a student ) Domain : It's a range . component : Attribute value of a tuple .
8. The secondary image function of the database : External mode / Mode image and mode / Internal mode image .
9. Relational algebra is an abstract query language : It is a relational operation to express the query . Three elements : Operands Operator Calculation results .
10. Specialized relational operations include : choice Projection Connect In addition to the operation .
11. Database insecurity : 1. Unauthorized users' malicious access to and destruction of the database 2. Important or sensitive data in the database is leaked . 3. Vulnerability of the security environment .
12. Database security settings :(1) The system first performs user identification according to the input user ID , Only legitimate users are allowed to enter the computer system .(2) For users who have entered the system , Database management system also has access control , Only users are allowed to perform legal operations .(3) The operating system will have its own protection (4) Finally, the data will be stored in the database in the form of password .
13. The security of the database mainly includes the scope : User identification Multilayer access control Audit View Data encryption .
14. User identification : Static password authentication Dynamic password authentication Biometric identification Smart card identification .
15. grant GRANT Take back REVOKE .
16. Database role : Is a named set of permissions related to database operations , Roles are sets of permissions .
17. The role of the database : Character creation Authorize roles Give a role to another role or user Recovery of role authority .
18. Only if the subject's license level is greater than or equal to the object's secret level , The subject can read the corresponding object . Only if the subject's license level is less than or equal to the object's secret level , The subject can write the corresponding object .
19. The basic idea of encryption is to encrypt the original data according to a certain algorithm — Plaintext . Transform to unrecognizable format ---- Ciphertext , So that people who don't know the decryption algorithm can't know the content of the data . Data encryption mainly includes storage encryption and transmission encryption .
20. Trigger is a special kind of event driven process defined by user on relational table .
21. Triggers are also called events - Conditions - Action rules .
22. The basic idea of normalization is to gradually eliminate the inappropriate parts of data dependency .
23. The data dictionary : It's a description of the data in the database , Metadata , Not the data itself . The data dictionary is set up in the requirement analysis stage , Constantly modify in the process of database design Enrich Perfect . It plays a very important role in database design .
24. Multi granularity blocking protocol : Locking a node means that all descendant nodes of the node are also locked with the same type .
25. Show blocked : It is a lock directly added to a data object at the request of a transaction . Implicit locking means that the data object is not locked independently , The data object is locked because its parent node is locked .
26. Intent locks : If you add intention lock to a node , It means that the lower node of the node is being locked .