[Database] Database System Concepts Basic Concepts

1 Basic Concepts

Data Data

Database DataBase

Database System DataBaseSystem

Database management system DataBaseManageSystem

Wherein the database system DBS = DB + database management system database DBMS + User / Administrators

 

2 development

• Database development: labor management system >> >> file database system
• Database systems and file systems fundamental difference: structured data
• A defect file system (database system these drawbacks are resolved w)
  • Data redundancy and inconsistency
  • Difficulity in accessing data
  • Data isolation
  • Integrity problems
  • Atomicity of updates
  • Concurrent access by multiple users
  • Security problems

 

 

3 two three-schema mappings

• View layer View Level-> Conceptual schema
  • And a user can see the data processing, are part of the global data
  • ER model

|| EC mapping maps

• Logical layer Logical Level-> Logical schema
  • Appreciated / management data from a global perspective, including the corresponding relationship constraint
  • Relational Model
  • Mesh model, hierarchical model, based on the data model objects, semi-structured data models, etc.

|| CI mapping maps

• Physical Layer Physical level-> Physical schema
  • The lowest level of data abstraction. Described in the data storage medium, comprising a storage path, storage, etc.
  • B * Tree Model

 

 

Wherein the layers are mapped from the bottom up to ensure the independence of the two -

• Physical data independence
  • Physical storage applications and user data in the database independent
  • When the physical storage changed, the user applications are not affected
• Logical data independence
  • User application database logical structure independent of each other
  • When the logical structure of data changes, the application is not changed.

 

Function 4 database

• The user's perspective
  • Database definition function --DDL
  • Database management functions --DML
    • Procedural DML
      • User specifies what data is required and how to get these data
    • Declarative DML
      • User specifies what data is required without specifying how to get those data
  • Database maintenance --DBA
• A systems perspective