What are some data restrictions in DBMS

1. Access to the database

Method 1. DBMS (Database Management System) ---- refers to MySQL SQL Server ORACLE etc.

Method 2. Use program access (ASP, JSP, VC ++, PHP, PowerBuilder), program call)) ODBC interface to access the database

2. Database (DB
An organized collection of data on companies and institutions in one computer

3. Database management system (DBMS)
Database + a set of tools for accessing and updating queries
DBMS functions:
Efficient scalability of data access
Reduce application development time
Data independence (physical independence / logical independence) (if the lower tier changes, the upper tier does not have to change, reducing the workload)
Data integrity and security (storing the data in the system helps protect the data)
Concurrent access and robustness (support of multi-user access requirements) (provision of a system protection mechanism in the event of a system failure)
Course:
File processing system –50
Network, hierarchical (network, hierarchical) - but the structure is complex, the computer power is insufficient and difficult to use - 60
relational model (relational database system)
RDBMS was displayed - 70 present
RDBMS goes to market 80
RDBMS technology mature-90
Object-oriented database system (OODBMS)
Object relational database system (ORDBMS)
Data warehousing, online analysis

4 file processing system VS database management system
Every system like Windows has a file processing system
A program is required for each file execution
Data is redundant and inconsistent (multiple file formats, repeated storage of information)
Release of data value keys, difficult to retrieve
Completeness:
Atomicity: Indivisible, refers to processes that either take place or do not take place, such as B. Transfers, but not in the file. Add one to do the transfer and then the system will fail
Simultaneous access: The database system can work, but the file cannot
Security: The database can be specific to all levels of operation

5 open source database system:
MySQL: The most popular open source small system database on the site

Data abstraction: (only if the data is displayed)
Different uses require different levels of representation
Physical Layer: Describe how the data will be stored
Logic Layer: Describe what data is stored in the database and what kind of relationship there is between the data
For example, type instructor = record
ID : char (5)
name : char (20)
dept_name : char (20)
salary : numeric (8,2) :
end:
View level: the application can hide the detailed information of the data type, and the view can hide the data information for security reasons (e.g. an employee's salary).


6 examples and samples

  1. Similar to the type (type) real column = variable, mode = type in a programming language

  2. Mode: The overall design of the database
    is similar to the type of information in programming
    Physical mode: The design of the database path described in the physical layer
    Logic mode: The design of the database described in the logic layer

  3. Example: Specific data that is stored in the database
    is similar to the value of a variable in the program

    The three levels have their own modes, and each level has an association. The general user will see these in the section above the water

7Logical independence and physical independence

  1. The two-stage mapping of the above three-layer mode makes it possible to change the structural definition of one of the three layers without affecting the structural definition of the higher layer, which guarantees physical and logical independence.

  2. Physical data independence: Change the physical layer without affecting the logical layer
    : The application depends on the logical structure
    : The application is independent of the data structure and storage
    : What to do when changing disks and heap, but the upper layer does not change, which is an important benefit of DBMS

  3. Independence from logical data: Changes in the logical structure of data do not affect the application
    : In general, independence from logical data is difficult to achieve because the application and the logical structure are heavily dependent on it

8 data model

  1. The data model is a collection of conceptual tools that correspond to the data type in programming.
    Data structure:
    Data relationship:
    Data restrictions:
    Data semantics

  2. Different levels of data abstraction require different models to describe


Database design steps

  1. Needs analysis:
    - What type of database, application, and business need to be running?

  2. Conceptual structure of the database design
    - Use the E-R model or similar parent model to build

  3. Logical structure of the database design
    - Transform the concept design into a data model recognized by the DBMS

  4. Structure optimization
    - Remove structural redundancy, check the standardization of abnormal structures and relationships

  5. Physical database design
    - Index, cluster and database optimization

  6. Create and test initial data
    - Enter the initial data and test
    - Identify different users and their roles

Entity Contact Model
Entity (object)
For example customer, account, bank
The entity is described by attributes
Contact: is the relationship between multiple entities
The connection between the customer and the bank consists, for example, of deposits and withdrawals


We can also display some information in the view plane (the information in the view plane can come from different tables).