01 Introduction

Purpose#

Relational Model
- 使用多张表存储数据和数据的关系，tables are also known as relations
- an example of record-based model, fixed-format records of several types, each table contains records of a particular type
- columns 对应的是 attributes of the record type
Entity-Relationship(E-R) Model
- a collection of basic objects, called entities
- widely used in database design
Semi-structured Data Model
- individual data items may have different sets of attrs
- .json and .xml
Object-Based Data Model
- allows procedures to be stored and executed

Physical level
- low-level 的数据结构，文件等
- describe how the data are actually stored
Logical level
- describe what data are stored in db, and what relationships exist among those data
- @Physical data independence: logical level 的用户无需关注 logical level 的简单结构在 physical level 的实现有多么复杂
View level
- DBMS may provide many views for the same database
- 客户不会需要查看 db 里的所有信息，所以只展示部分信息

IMG-DB 01 Introduction-20250225132259045.webp

@instance: The collection of information stored in the database at a particular moment is an instance of the database
- 数据库的快照
@Schema: The overall design of the database
- physical schema: design at physical level
  - hidden beneath the logical schema
  - usually can be changed easily without affecting application programs
- logical schema: design at logical level
  - most important
- subschemas: at view level

Data-Definition Language (DDL): 表述 schema
- data storage and definition
- integrity constrs
  - domain constr
  - referential integrity
  - authorization
    - read
    - insert
    - update
    - delete
Data-Manipulation Language (DML): 表述 query 和更新操作
- Procedural DML
- Declarative DML
二者并非独立，而是结合成 SQL language
- 非 turing complete