01 概论

4个基本概念

Database(DB):

• a collection of interrelated(相互关联的) data
• stored as files

Database management system(DBMS)

consisting of

• DB
• Programs to access DB

Database system(DBS)

• Same definition as DBMS
• DBS and DBMS are used interchangeably(可交换地)

DBS manage collections of data:

• Highly valuable
• Relatively large
• Multiple users, accessed by at the same time

DBS can manage a large collection of data with various forms and structures.

DBMS provides an environment for store and retrieve(取回) information

• definition of structures for storage of information
• data manipulation(操作) mechanisms
• data safety mechanisms

Database application system(DBAS)

• DB + DBMS + Application programs + Users/Administers

DBAS built directly on file systems, leading to:

• Data redundancy(冗余) and inconsistency(不一致)
• Difficulty in accessing data
• Data isolation
• Integrity(完整性) problems

Purpose of DBS

• Atomicity of updates
• Concurrent access by multiple users
• Security problems

DBS offer solutions to all the above problems

View of Data

• data models
  • conceptual tools for describing:
    • data, data relationships
    • data semantics, and consistency constraints
• data modeling
  • organize application data, according to data model, by data abstraction
• data abstraction
  • database modeling mechanism
  • hide complexity of data structures to represent data through view-logical-physical levels of data abstraction

Definition of data model

• 对数据组织与管理/使用方式的抽象描述，包括
  • 数据组织的语法定义，如数据项、数据项之间的联系
  • 数据组织的语义，如完整性约束
  • 数据操作 程序 = 数据结构+算法

Relation model

• Entity-Relationship data model(mainly for database design)
• Object-based data models(Object-oriented and Object-relational)
• Semi-structured data model(XML)