Database review (i)--Introduction to the database

I. Overview of the database system

The database system includes:

1. Data

2. Database

3. Database management System (DBMS): System software, main functions: Data definition function (DDL), data organization, storage and management, data manipulation function DML, database transaction management and operation management

, the establishment and maintenance of the database, and the communication function between its software.

The development of data management technology: Database System Management, file System management, human management

Two. Data model

The abstraction of the real world

Classification:

A: Conceptual model: involves concepts: Entities, attributes, codes (keys), domains, entities (entities with the same attributes put together, such as: Student (school number, name, gender ...) ), Entity sets (similar entities), contact

Conceptual model representation: E-r Diagram, Entity-Contact method

Categories: Relational data models, hierarchical data models, mesh data models

Two: Logical model:

Three: Physical model:

　　

A data model is a set of tightly defined concepts: static characteristics of data, dynamic characteristics, and integrity constraints

Corresponding, the data model is usually composed of three parts, data structure, operation and integrity constraint.

Relational Data Model:

Data structures: Two-dimensional tables: relationships, tuples, attributes, codes, domains, components, relational patterns

Manipulation of the data model: collection operations, objects, and results are all relationships

Integrity constraints: Entity integrity, referential integrity, user-defined integrity

Mode of the Data system:

External mode

Internal mode

Mode

Data independence:

External mode/mode image

Mode/Internal mode image

Guaranteed Data Independence

　　

Database review (i)--Introduction to the database