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 2

Table Contents Database system environment Database system architecture Data independence Database users Data dictionary Advantages and disavantages of database system 3

File System 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 4

File Processing System Environment Files Operating system Application programs 5

Database system 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 6

Database processing system environment Application program DBMS Operating system Database 7

Database processing using DBMS Staff recruitment system Customers’ orders Sales accounting Department2 Department1 Department3 Employee data Product Customer DBMS Database 8

Database A shared collection of interrelated data. A collection of data stored in a standardized format and designed to be shared by multiple users. A collection of persistent related data of interest of a specific enterprize. Database contains information about a particular enterprise. 9

Units of data Database 19 M Sasin 4702888 18 F Amporn 4702777 Age Sex File Record Field Database Student file : 19 M Sasin 4702888 18 F Amporn 4702777 Age Sex Name Student ID 10

Units of data Physical level Unit of data used by the hardware of computers. Bit Byte Word 11

Units of data Logical level Unit of data used or viewed by the users. Field Record File Database 12

Units of data database file record field byte bit 01001011 (letter K in ASCII) Amporn 4720777, Amporn, F, 18 Listing of all students in student file Student and teacher files 13

Database management system (DBMS) 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. 14

Database users Users in database environment are people whose jobs involve the day-to-day use of large database. 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. 15

Table Contents Database system environment Database system architecture Data independence Database users Data dictionary Advantages and disavantages of database system 16

Simplified view of database system User1 User2 User3 User4 User work area Physical database Logical database Physical level Logical level Externalal level 17

External level เป็นสถาปัตยกรรมข้อมูลระดับนอกสุด ใกล้ชิดกับผู้ใช้ฐานข้อมูลมากที่สุด เพราะเป็นระดับที่กล่าวถึงมุมมองข้อมูลของผู้ใช้แต่ละคน (user view) ผู้ที่เกี่ยวข้องคือ user ที่ใช้ฐานข้อมูล 18

Logical level เป็นสถาปัตยกรรมข้อมูลระดับที่อยู่ระหว่าง Internal กับ External ทำหน้าที่ถ่ายทอดรูปแบบของ Physical Level ให้อยู่ในรูปแบบที่สามารถเข้าใจได้ง่าย (Logical Structure) ผู้ที่เกี่ยวข้องกับข้อมูลในระดับนี้คือ DBA 19

Physical level เป็นสถาปัตยกรรมฐานข้อมูลระดับในสุด ซึ่งอธิบายโครงสร้างของการจัดเก็บข้อมูลในเชิงกายภาพ (Physical Structure) ผู้ที่เกี่ยวข้องกับระดับนี้คือ DBA และ System Administrator 20

Example Physical Level สถาปัตยกรรมระบบฐานข้อมูลทั้ง 3 ระดับ สามารถอธิบายได้โดยใช้ ฐานข้อมูลระบบงานสินค้าคงคลัง (northwind) ดังนี้ Physical Level ฐานข้อมูล Northwind เก็บอยู่ในไฟล์ที่ชื่อว่า northwind.mdb ซึ่งเป็นไฟล์ของโปรแกรม MS Access ทำงานอยู่บนระบบปฏิบัติการ MS Windows 95/98 เก็บอยู่ใน directory c:\program files\microsoft office\samples บน Hard Disk ณ ตำแหน่ง Sector 84A6, Track 15, Cylinder 8 เป็นต้น 21

Example External Level ฐานข้อมูล Northwind แบ่งให้พนักงานแผนกต่าง ๆ มองเห็นได้ต่างกัน ดังนี้คือ พนักงานฝ่ายขาย มองเห็นข้อมูลในCaregories, Orders, Order Details, Products, Categories พนักงานฝ่ายบุคคล มองเห็นข้อมูลใน Employees, Orders ผู้จัดการทั่วไป (GM) มองเห็นข้อมูลทั้งหมด 22

Example Logical Level ฐานข้อมูล Northwind ประกอบด้วย 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, 23

Simplified view of database system DBA(s)/Programmers/Naive users Programs/Query Language Programs/Query Processor Programs to access stored data Data dictionary Users’ database 24

Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system 25

Database users Application programmers Write application programs and interact DBMS through database language. Database administrator 26

Database administrator Responsible for all the activities of the database system environment. Must have a good understanding of the enterprise’s information resources and needs. 27

Database administrator 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 28

Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system 29

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. 30

Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system 31

Data dictionary The data dictionary or system catalog contains metadata Metadata means “data about the data” 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. 32

Data dictionary The data dictionary can be regarded as a database in its own right, but it is the system database rather than user database. The data in the data dictionary should be integrated into a database with the same structure as the user database. It should certainly be possible to query the data dictionary just like the users’ database. 33

Example Data dictionary 34

Example Data in Database 35

Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system 36

Advantages of database approach Providing a solution to basic data storage and retrieval. Providing flexibility and availability of up-to- minute information. Reducing data redundancy. Obtaining data consistency. Sharing of data. 37

Advantages of database approach (continue) 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. 38

Disadvantages of database approach 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 39