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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 2 Table Contents Database system environment Database system architecture Data independence Database users Data dictionary Advantages and disavantages of database system Introduction to 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 Introduction to Database System 4 File Processing System Environment Application programs Operating system Files Introduction to Database System 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 Introduction to Database System 6 Database processing system environment Application program DBMS Operating system Database Introduction to Database System 7 Database processing using DBMS Employee data Customer data Product data DBMS Staff recruitment system Department1 Customers’ orders system Department2 Sales accounting system Department3 Database Introduction to Database System 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. Introduction to Database System 9 Units of data File Database Record Field Student file : Student ID Name Sex Age 4702777 Amporn F 18 4702888 Sasin M 19 Introduction to Database System 10 Units of data Physical level Unit of data used by the hardware of computers. – – – Bit Byte Word Introduction to Database System 11 Units of data Logical level Unit of data used or viewed by the users. – – – – Field Record File Database Introduction to Database System 12 Units of data database Student and teacher files file Listing of all students in student file record field byte bit Introduction to Database System 4720777, Amporn, F, 18 Amporn 01001011 (letter K in ASCII) 0 or 1 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. Introduction to Database System 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. Introduction to Database System 15 Table Contents Database system environment Database system architecture Data independence Database users Data dictionary Advantages and disavantages of database system Introduction to Database System 16 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 Introduction to Database System 17 External level เป็ นสถาปัตยกรรมข้อมูลระดับนอกสุ ด ใกล้ชิดกับ ผูใ้ ช้ฐานข้อมูลมากที่สุด เพราะเป็ นระดับที่กล่าวถึง มุมมองข้อมูลของผูใ้ ช้แต่ละคน (user view) ผูท้ ี่ เกี่ยวข้องคือ user ที่ใช้ฐานข้อมูล Introduction to Database System 18 Logical level เป็ นสถาปัตยกรรมข้อมูลระดับที่อยูร่ ะหว่าง Internal กับ External ทาหน้าที่ถ่ายทอดรู ปแบบ ของ Physical Level ให้อยูใ่ นรู ปแบบที่สามารถ เข้าใจได้ง่าย (Logical Structure) ผูท้ ี่เกี่ยวข้องกับ ข้อมูลในระดับนี้คือ DBA Introduction to Database System 19 Physical level เป็ นสถาปัตยกรรมฐานข้อมูลระดับในสุ ด ซึ่งอธิบาย โครงสร้างของการจัดเก็บข้อมูลในเชิงกายภาพ (Physical Structure) ผูท้ ี่เกี่ยวข้องกับระดับนี้คือ DBA และ System Administrator Introduction to Database System 20 Example สถาปั ตยกรรมระบบฐานข้อมูลทั้ง 3 ระดับ สามารถอธิบายได้โดยใช้ ฐานข้อมูลระบบงานสิ นค้าคงคลัง (northwind) ดังนี้ Physical Level – – – 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 Introduction to Database System 21 Example External Level ฐานข้อมูล Northwind แบ่งให้พนักงานแผนกต่าง ๆ มองเห็น ได้ต่างกัน ดังนี้คือ – – – พนักงานฝ่ ายขาย มองเห็นข้อมูลในCaregories, Orders, Order Details, Products, Categories พนักงานฝ่ ายบุคคล มองเห็นข้อมูลใน Employees, Orders ผูจ้ ดั การทัว่ ไป (GM) มองเห็นข้อมูลทั้งหมด Introduction to Database System 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, Introduction to Database System 23 Simplified view of database system DBA(s)/Programmers/Naive users Programs/Query Language Programs/Query Processor Programs to access stored data Data dictionary Introduction to Database System Users’ database 24 Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system Introduction to Database System 25 Database users – – Application programmers Write application programs and interact DBMS through database language. Database administrator Introduction to Database System 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. Introduction to Database System 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 Introduction to Database System 28 Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system Introduction to 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. Introduction to Database System 30 Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system Introduction to 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. Introduction to Database System 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. Introduction to Database System 33 Example Data dictionary Introduction to Database System 34 Example Data in Database Introduction to Database System 35 Table Contents Database system environment Database system architecture Database users Data independence Data dictionary Advantages and disavantages of database system Introduction to Database System 36 Advantages of database approach 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. Introduction to Database System 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. Introduction to Database System 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 Introduction to Database System 39