Transcript Introduction to Database System

Introduction to Database System
Chapter 2:
Database Architecture
Adisak Intana
Lecturer
Table Contents
Database system environment
Database system architecture
Data independence
Database users
Data dictionary
Advantages and disavantages of database system
Introduction to Database System
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Table Contents
Database system environment
Database system architecture
Data independence
Database users
Data dictionary
Advantages and disavantages of database system
Introduction to Database System
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File System
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A computerized data processing environment which is
composed of four major parts :
Hardware
The computer hardware : CPU, mainmemory, and I/O
devices
Software
– Application programs
Data is in a collection of independent files
Users
– Naive users
– Application programers
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File Processing System Environment
Application programs
Operating system
Files
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Database system
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A computerized data processing environment which is
composed of four major parts :
Hardware
The computer and the secondary storage devices
Software
Data is in a collection of related files in the form of
database
Users
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Database processing system
environment
Application program
DBMS
Operating system
Database
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Database processing using DBMS
Employee
data
Customer
data
Product
data
DBMS
Staff recruitment
system
Department1
Customers’ orders
system
Department2
Sales accounting
system
Department3
Database
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Database

A shared collection of interrelated data.
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A collection of data stored in a standardized format and
designed to be shared by multiple users.
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A collection of persistent related data of interest of a
specific enterprize.
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Database contains information about a particular
enterprise.
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Units of data
File
Database
Record
Field
Student file :
Student ID
Name
Sex
Age
4702777
Amporn
F
18
4702888
Sasin
M
19
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Units of data

Physical level
Unit of data used by the hardware of
computers.
–
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–
Bit
Byte
Word
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Units of data

Logical level
Unit of data used or viewed by the users.
–
–
–
–
Field
Record
File
Database
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Units of data
database
Student and teacher files
file
Listing of all students in
student file
record
field
byte
bit
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4720777, Amporn, F, 18
Amporn
01001011 (letter K in ASCII)
0 or 1
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Database management system
(DBMS)
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A collection of programs that enables users to modify
and extract information from a database.
A suite of programs which typically manage large
structured sets of persistent data and offering ad hoc query
facilities to many users.
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Database users
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Users in database environment are people whose jobs
involve the day-to-day use of large database.
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Users are differentiated by the way they expect to
interact with the database management system.
– Naive users
Invoke and use the application programs that have
been written for specific tasks.
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Table Contents
Database system environment
Database system architecture
Data independence
Database users
Data dictionary
Advantages and disavantages of database system
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Simplified view of database system
User1
User2
User3
User4
User
User
User
User
work
work
work
work
area
area
area
area
Logical database
Externalal level
Logical level
Physical database
Physical level
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External level
เป็ นสถาปัตยกรรมข้อมูลระดับนอกสุ ด ใกล้ชิดกับ
ผูใ้ ช้ฐานข้อมูลมากที่สุด เพราะเป็ นระดับที่กล่าวถึง
มุมมองข้อมูลของผูใ้ ช้แต่ละคน (user view) ผูท้ ี่
เกี่ยวข้องคือ user ที่ใช้ฐานข้อมูล
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Logical level
เป็ นสถาปัตยกรรมข้อมูลระดับที่อยูร่ ะหว่าง
Internal กับ External ทาหน้าที่ถ่ายทอดรู ปแบบ
ของ Physical Level ให้อยูใ่ นรู ปแบบที่สามารถ
เข้าใจได้ง่าย (Logical Structure) ผูท้ ี่เกี่ยวข้องกับ
ข้อมูลในระดับนี้คือ DBA
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Physical level
เป็ นสถาปัตยกรรมฐานข้อมูลระดับในสุ ด ซึ่งอธิบาย
โครงสร้างของการจัดเก็บข้อมูลในเชิงกายภาพ (Physical
Structure) ผูท้ ี่เกี่ยวข้องกับระดับนี้คือ DBA และ System
Administrator
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Example
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สถาปั ตยกรรมระบบฐานข้อมูลทั้ง 3 ระดับ สามารถอธิบายได้โดยใช้
ฐานข้อมูลระบบงานสิ นค้าคงคลัง (northwind) ดังนี้

Physical Level
–
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ฐานข้อมูล Northwind เก็บอยูใ่ นไฟล์ที่ชื่อว่า northwind.mdb ซึ่งเป็ นไฟล์ของโปรแกรม
MS Access
ทางานอยูบ่ นระบบปฏิบตั ิการ MS Windows 95/98
เก็บอยูใ่ น directory c:\program files\microsoft office\samples บน Hard Disk ณ
ตาแหน่ง Sector 84A6, Track 15, Cylinder 8 เป็ นต้น
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Example
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External Level ฐานข้อมูล Northwind แบ่งให้พนักงานแผนกต่าง ๆ มองเห็น
ได้ต่างกัน ดังนี้คือ
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พนักงานฝ่ ายขาย มองเห็นข้อมูลในCaregories, Orders, Order Details, Products,
Categories
พนักงานฝ่ ายบุคคล มองเห็นข้อมูลใน Employees, Orders
ผูจ้ ดั การทัว่ ไป (GM) มองเห็นข้อมูลทั้งหมด
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Example
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Logical Level ฐานข้อมูล Northwind ประกอบด้วย
–
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Tables คือ Categories, Customers, Employees, Order Details, Orders, Products, Shippers
และ Suppliers
Queries คือ Category Sales for 1995, Current Product List, Employee Sales by Country,
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Simplified view of database
system
DBA(s)/Programmers/Naive users
Programs/Query Language
Programs/Query Processor
Programs to access stored data
Data dictionary
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Users’ database
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Table Contents
Database system environment
Database system architecture
Database users
Data independence
Data dictionary
Advantages and disavantages of database system
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Database users
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Application programmers
Write application programs and interact DBMS
through database language.
Database administrator
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Database administrator
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Responsible for all the activities of the
database system environment.
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Must have a good understanding of the
enterprise’s information resources and
needs.
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Database administrator
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Database administrator's duties include :
– Define the schema
– Define storage structure and access method
– Modify schema and physical organization
– Granting user authority to access the database
– Specifying integrity constraints
– Acting as liaison with users
– Monitoring performance and responding to
changes in requirements
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Table Contents
Database system environment
Database system architecture
Database users
Data independence
Data dictionary
Advantages and disavantages of database system
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Database independence
 The ability to change the description of a database
structure at one level of the database system
architecture without having to change the
description at the next higher level database
structure.
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Table Contents
Database system environment
Database system architecture
Database users
Data independence
Data dictionary
Advantages and disavantages of database system
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Data dictionary
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The data dictionary or system catalog contains metadata
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Metadata means “data about the data”
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This metadata is the definitions of the structure, data type,
integrity constraints, etc. of the database and other objects
in the DBMS rather than the users’ raw data.
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Data dictionary
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The data dictionary can be regarded as a database in its own
right, but it is the system database rather than user
database.
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The data in the data dictionary should be integrated into a
database with the same structure as the user database.
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It should certainly be possible to query the data dictionary
just like the users’ database.
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Example Data dictionary
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Example Data in Database
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Table Contents
Database system environment
Database system architecture
Database users
Data independence
Data dictionary
Advantages and disavantages of database system
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Advantages of database
approach
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Providing a solution to basic data storage and
retrieval.
Providing flexibility and availability of up-tominute information.
Reducing data redundancy.
Obtaining data consistency.
Sharing of data.
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Advantages of database approach
(continue)
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Standard can be enforced.
Ad hoc queries are possible.
Ease of application programs development.
Reduce application program development time.
Uniform security, privacy, and integrity can be
applied.
Obtaining data independence.
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Disadvantages of database approach
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High cost
– Conversion from file processing to
DBMS
– More sophisticated hardware and
software
– Higher operating costs (personnel)
Complexity of DBMS administration
Vulnerability to failure
Difficulty of recovering & securing data
assets
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