Drawbacks of Using File Systems to Store Data
- Data redundency(冗余) and inconsistency
- Difficulty in accessing dataneed :
Need to write a new program to carry out each new task - Data isolation:文件格式
- Intefrity problems:
Hard to add new constraints or changeexisting ones - Atomicity of updates:
Failures may leave database in an inconsistent state with partial updates carried out - Concurrent(同时) access by multiple users
- Security problems:
Hard to provide user access to some, but to all, data
Levels of Abstraction
Physical level
Logical level
View level
Schema(模式)
Physical schema
Logical schema
Instance(实例)
Physical Independence
A collection of tools for describing
Data
Data relationships
Data sementics(语义)
Data constraints
Relational model
Entity-Relationship data model
Object-based data model
Semistructured data model(XML)
Two classes of languages:
Procsdural
Declarative
Data Definition Language(DDL)
DDL compiler generate a set of tables stored in a data dictionary
ER Model
Transaction Management
Database Architecture
Centrailized
Client-server
Browser-server
Parallel
Distributed
Database Administer(DBA)
