2013 Fall2013 Fall 11

Chapter 9:Chapter 9: The Client/Server The Client/Server

Database EnvironmentDatabase Environment

楊立偉教授台灣大學工管系

註 註 :: 於於 1111 版為版為 Chapter 8Chapter 8

Chapter 9 22

Client/Server SystemsClient/Server Systems

Networked computing model Networked computing model 網路運算模型網路運算模型 Processes distributed between clients and Processes distributed between clients and

servers servers 將要處理的工作散在將要處理的工作散在 ClientClient 與與 ServerServer Client–Workstation (usually a PC) that Client–Workstation (usually a PC) that

requests and uses a servicerequests and uses a service Server–Computer (PC/mini/mainframe) Server–Computer (PC/mini/mainframe)

that provides a servicethat provides a service For DBMS, server is a database serverFor DBMS, server is a database server

Chapter 9 33

Application Logic in C/S Application Logic in C/S SystemsSystems

GUI(Graphic User Interface)

Procedures, functions,programs

DBMS activities

Processing Logic Processing Logic 處理邏輯處理邏輯 I/O processingI/O processing Business rulesBusiness rules Data managementData management

Storage Logic Storage Logic 儲存邏輯儲存邏輯 Data storage/retrievalData storage/retrieval

Presentation Logic Presentation Logic 呈現邏呈現邏輯輯 Input–keyboard/mouseInput–keyboard/mouse Output–monitor/printerOutput–monitor/printer

Chapter 9 44

3 types of Client/Server 3 types of Client/Server ArchitecturesArchitectures

1.File Server Architecture1.File Server Architecture

2.Database Server 2.Database Server

ArchitectureArchitecture

3.Three-tier Architecture3.Three-tier Architecture

Client does extensive processing

Client does little processing

Chapter 9 55

1. File Server Architecture1. File Server Architecture

All processing is done at the PC that requested All processing is done at the PC that requested the data the data

Entire files are transferred from the server to the Entire files are transferred from the server to the client for processing client for processing Ex. 利用網路芳鄰分享 MDB 檔

Problems:Problems: Huge amount of data transfer on the networkHuge amount of data transfer on the network Each client must contain full DBMS Each client must contain full DBMS

Heavy resource demand on clientsHeavy resource demand on clients Client DBMSs must recognize shared locks, integrity checks, Client DBMSs must recognize shared locks, integrity checks,

etc.etc.

FAT CLIENT

Chapter 9 66

Figure 9-2 File server model

FAT FAT CLIENTCLIENT

Chapter 9 77

2. Two-Tier Database Server 2. Two-Tier Database Server ArchitecturesArchitectures

Client is responsible for Client is responsible for I/O processing logic I/O processing logic Some business rules logicSome business rules logic

Server performs all data storage Server performs all data storage and access processing and access processing DBMS is only on serverDBMS is only on server

Chapter 9 88

Advantages of Two-Tier Advantages of Two-Tier ApproachApproach

Clients do not have to be as powerfulClients do not have to be as powerful Greatly reduces data traffic on the Greatly reduces data traffic on the

networknetwork Improved data integrity since it is all Improved data integrity since it is all

processed centrallyprocessed centrally Stored procedures : performs some Stored procedures : performs some

business rules done on server business rules done on server

把較常用或重要的程序預先寫好放在把較常用或重要的程序預先寫好放在 DBMSDBMS 內內

Chapter 9 99

Advantages of Advantages of Stored ProceduresStored Procedures

Compiled SQL statements Compiled SQL statements 編譯後執行編譯後執行快快

Reduced network traffic Reduced network traffic 佔較少的網路佔較少的網路流量流量

Improved security Improved security 安全性較高安全性較高 Improved data integrity Improved data integrity 資料完整性較資料完整性較

高高 Thinner clients Thinner clients 前端運算量較少前端運算量較少

Chapter 9 1010

Figure 9-3 Database server architecture (two-tier)

ThinneThinner r clientsclients

DBMS DBMS only on only on serverserver

Chapter 9 1111

3. Three-Tier Architectures3. Three-Tier Architectures

Thin Client PC just for user interface and a little application

processing. Limited or no data storage (sometimes no hard drive) 例如 : Web Browser

GUI interface (I/O processing)

Browser

Business rules Web Server

Data storage DBMS

ClientClient

Application serverApplication server

Database serverDatabase server

Chapter 9 1212

Figure 9-4a Generic three-tier architecture

Thinnest Thinnest clientsclients

Business rules Business rules on separate on separate serverserver

DBMS only DBMS only on DB serveron DB server

Chapter 9 1313

Advantages of Three-Tier Advantages of Three-Tier ArchitecturesArchitectures

Scalability Scalability ( 在佈署與效能上 ) 具擴充性 Technological flexibility Technological flexibility 具技術彈性 Long-term cost reduction Long-term cost reduction 長期低本降

低 Better match of systems to business Better match of systems to business

needs needs 較符合企業所需 Reduced risk Reduced risk 風險降低

Chapter 9 1414

Application PartitioningApplication Partitioning

Placing portions of the application Placing portions of the application code in different locations (client vs. code in different locations (client vs. server) AFTER it is written server) AFTER it is written 重新切分程重新切分程式執行的位置式執行的位置

AdvantagesAdvantages Improved performanceImproved performance Improved interoperabilityImproved interoperability Balanced workloadsBalanced workloads

Chapter 9 1515

Common Logic Common Logic DistributionsDistributions

Figure 9-5a Two-tier client-server environments

Figure 9-5b n-tier client-server environment

Processing logic could be at client, server, or both

Processing logic will be at application server or Web server

Chapter 9 1616

Role of the Mainframe Role of the Mainframe 大型大型主機主機

Mission-criticalMission-critical legacy systems tend to remain on legacy systems tend to remain on mainframes mainframes

When moving mission critical systems from mainframe When moving mission critical systems from mainframe to distributed client/server systemsto distributed client/server systems

例如例如 : : 銀行核心系統的移轉銀行核心系統的移轉 Determining which code belongs on server vs. clientDetermining which code belongs on server vs. client Identifying potential conflicts with code from other applicationsIdentifying potential conflicts with code from other applications Ensuring sufficient resources exist for anticipated loadEnsuring sufficient resources exist for anticipated load

Rule of thumb Rule of thumb 移轉的經驗法則移轉的經驗法則 Mainframe for centralized data that does not need to be movedMainframe for centralized data that does not need to be moved Client for data requiring frequent user access, complex Client for data requiring frequent user access, complex

graphics, and user interfacegraphics, and user interface

Chapter 9 1717

Benefits of Moving to Benefits of Moving to Client/Server ArchitectureClient/Server Architecture

Staged delivery of functionality speeds Staged delivery of functionality speeds deployment deployment 功能可分階段完成功能可分階段完成

GUI ease application use GUI ease application use 將使用者界面與應用分將使用者界面與應用分離離

Flexibility and scalability facilitates business Flexibility and scalability facilitates business process reengineering process reengineering 更容易擴充 具有彈性更容易擴充 具有彈性

Reduced network traffic Reduced network traffic 只傳處理過的資料只傳處理過的資料 Facilitation of Web-enabled applicationsFacilitation of Web-enabled applications

易於轉為易於轉為 WebWeb 或行動應用或行動應用

Chapter 9 1818

Middleware Middleware 中介軟體中介軟體 Software that allows an application

to interoperate with other software No need for programmer/user to

understand internal processing Accomplished via Application

Program Interface (API)

The “glue”“glue” that holds client/server applications together

Chapter 9 1919

Database MiddlewareDatabase Middleware ODBCODBC–Open Database Connectivity–Open Database Connectivity

Most DB vendors support thisMost DB vendors support this

JDBCJDBC–Java Database Connectivity–Java Database Connectivity可視為可視為 JavaJava 版的版的 ODBCODBC Special Java classes that allow Java Special Java classes that allow Java

applications/applets to connect to databasesapplications/applets to connect to databases

OLE-DBOLE-DB Microsoft enhancement of ODBCMicrosoft enhancement of ODBC

Chapter 9 2020

Using ODBC to Link External Using ODBC to Link External Databases Stored on a Database Databases Stored on a Database

ServerServer Open Database Connectivity (ODBC)Open Database Connectivity (ODBC)

API provides a common language for API provides a common language for application programs to access and process application programs to access and process SQL databases independent of the particular SQL databases independent of the particular RDBMS that is accessedRDBMS that is accessed

Required parameters:Required parameters: ODBC driver ODBC driver Back-end server nameBack-end server name Database nameDatabase name User id and passwordUser id and password

Additional information:Additional information: Data source name (DSN)Data source name (DSN) Windows client computer nameWindows client computer name Client application program’s executable nameClient application program’s executable name

Chapter 9 2121

ODBC Architecture ODBC Architecture (Figure 9-6)(Figure 9-6)

Each DBMS has its own ODBC-compliant driver

Client does not need to know anything about the DBMS

Application Program Interface (API) provides common interface to all DBMSs

Chapter 9

實作 : 實際設定一個 DSN ( 適用 Windows 作業系統 )

控制台→系統管理工具→資料來源 (ODBC) 選「系統資料來源名稱」→選「新增」 選一個適當的驅動程式 (Driver)

Chapter 9

實際設定一個 DSN ( 續 ) 填入所需資料並選取 Access 的 MDB 檔案，確定即可

Chapter 9

使用 ODBC 資料來源 以 MS Access 為例，選檔案→取得外部資料→匯入 選取 ODBC 來源，選取所需要的 DSN 即可

適用所有支援 ODBC資料來源的應用程式

Chapter 9

Web/DB Application Web/DB Application ComponentsComponents

Database server – hosts the DBMSDatabase server – hosts the DBMS e.g. Oracle, MS SQL Server, MS Access, MySQLe.g. Oracle, MS SQL Server, MS Access, MySQL

Web server – receives and responds to browser Web server – receives and responds to browser requests using HTTP protocolrequests using HTTP protocol e.g. Apache, MS IIS (Internet Information Services)e.g. Apache, MS IIS (Internet Information Services)

Application server – software for creating dynamic Application server – software for creating dynamic web sitesweb sites e.g. MS ASP .NET framework, Java EE, PHPe.g. MS ASP .NET framework, Java EE, PHP

Web browser – client program that sends web Web browser – client program that sends web requests and receives web pagesrequests and receives web pages e.g. Internet Explorer, Firefox, Safari, Google Chromee.g. Internet Explorer, Firefox, Safari, Google Chrome

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Chapter 9

Static page requests Static page requests .htm or .html requests handled by the Web server.htm or .html requests handled by the Web server

Dynamic page requestsDynamic page requests .jsp, .aspx, and .php requests are routed to the .jsp, .aspx, and .php requests are routed to the

application serverapplication server Server-side processing by JSP servlet, ASP .NET Server-side processing by JSP servlet, ASP .NET

application, or PHPapplication, or PHP Database access via JDBC, ODBC, ADO .NET, or Database access via JDBC, ODBC, ADO .NET, or

other database middlewareother database middleware

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Chapter 92727

Figure Information flow in a three-tier architecture

No server side processing, just a page return

Server side processing, including database access

…also *.aspx or *.php

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