Database System

Database

1、Introduction to Database System

1.1 Basic Concepts —— Data、Database、DBMS、DBS

Data

• the basic object stored in the computer
• the symbol record depicting (描写、刻画) the objects that exists objectively
• Data type (digit, text, graph, image, audio, video, etc)

Database(DB)

A shared collection of logically related data, and a description of this data, designed to meet the information needs of an organization.

There're two types of data:

• User data, Logically related data comprises entities, attributes, and relationships of an organization’s information. e.g. Grade=90
• Metadata (元数据) (System catalog , data dictionary) is the ‘data about data’and provides description of data, e.g. int grade

Database Management System (DBMS)

A software system that enables users to define, create, and maintain and control access to this database.

The DBMS is the software that interacts with the users’ application program and the database.

DBMS provides the following functions and service:

• Data definition language (DDL).
  
  • Allows the user to describe the objects in database
  • Permits users to specify data types, structures and any data constraints on the data to be stored in the DB
• Data Manipulation Language (DML)
  
  • Provides basic data operations (Data Retrieval, insert，delete and update) on data held in the database
    
    • Procedural DML: allows user to tell system exactly how to manipulate data
    • Non-Procedural DML :allows user to state what data is needed rather than how it is to be retrieved
• It provides controlled access to database, it may include:
  
  • A security system, which prevents unauthorized users accessing the DB
  • An integrity system, which maintain the consistency (一致性) of stored data when being stored more than once
    
    • DB integrity refers to the correctness, validity and consistency of the stored data. integrity = constraints
  • A concurrency control system, which allows shared access of the DB
  • A recovery control system, which restores the database to a previous consistent state following a hardware or software failure
• A view mechanism
  
  • Provides users with only the data they want or need to use
  • Customize the appearance of the DB
  • Provides a level of security. Exclude data that some users should not see
  • Services to Promote Data Independence (between data and program)
• Utility (功用) Services
  
  • Load data, Monitor, Statistic & Analyse, Reorganize

DBS

computer system using DB technique,consisting of

• DB
• DBMS
• Application system
• DBA（Database Administrator）