1999 年 5 月 shinewave international introduction to n-tier architecture

1999 5年月Shinewave International

Introduction to N-Tier Architecture


3-tier架構(Presentation,Logic,DB Access)

Application(Browser)

ActiveXControl

Client Site(UI/Win95)

ApplicationServer

DBServer

Middle Site(MTS/NT)

Server Site (SQL/NT)

ServerApplication


N-tier 示意圖

Browser

WebLoad

BalanceBrowserBrowser

WebServer

WebServer

WebServer

APServer

APServer

APServer

APServer

MessageQueue

DBServer

OtherSystem


Gaining a Perspective

• Approach• Focus Primarily on Interactive Applications• Start With a Bit of History• Explain Emergence of Web App Servers• Explain Transition to App Servers• Explain Where ND Fits



A Bit of History


Gaining a Perspective:Bit of History

• Timeline• 70’s-Early 90’s: No Widespread Access to Internet• 70’s-80’s: Green Screen Era• Late 80’s: Dawn of the PC Era• Mid-90’s: Internet Emerges• Meantime, Client/Server Evolves• Late 90’s: HTTP/HTML Spill Over into Corporate Intranets



• Timeline

1970'sGreen Screen

TerminalsDominate

1980's-Early '90'sPC's and GUIs

Dominate

Mid-90'sWeb

Explodes

TodayBrowserClients

TomorrowDiverseClients



• 70’s-80’s: Age of the Green Screen

Monitor

327x

IBM Mainframe- Proprietary OS: S370- Classic TP Monitor: CICS- Proprietary Databases

Monitor

327x

Green Screen Terminals:- Dedicated to Specific Backend System

- No Local Software

Monitor

Other TerminalsMinicomputer- Proprietary OS- Proprietary Databases



• 70’s-80’s: Age of the Green Screen• Backend Systems: Diverse OS’s, Classic TP Monitors, DBs,

Closed Apps• Terminals Dedicated to Specific Systems• Difficult to Tie Together Diverse Backend Systems• No GUI Capability on Client• No Software Distribution Cost to Clients• Technologies Limited to Business Networks



• Late 80’s-Mid 90’s: PC Era

Mac

UNIX Workstation

LAN Server

PC LAN

PC

AppletalkLAN

Mainframe

TCP/IPLAN

DB

Tandem

DB

Diverse Backend Databases:- PC Clients Connect to Each DB

- Integration Business Logic on Client



• Late 80’s-Mid 90’s: PC Era• GUI Builders

• Sophisticated GUI Building Tools (RAD)• Easy-to-Use Tools• OOP Emerges on Client• Attempts at Cross Platform• Run Terminal Emulators on Client



• Late 80’s-Mid 90’s: PC Era• Client Connections to RDBMS and Backend Services

• 2 Tier• Client App Uses RDBMS Client APIs• Inefficient Use of DB Connections• Places Lots of Business Logic on Client• Client App’s Responsibility to Integrate Diverse Backend

Systems



• Late 80’s-Mid 90’s: PC Era• Client Connections to New Generation TP Monitors

TCP/IPLAN

PC

Mainframe

Tandem

TP Monitors:- PC Clients Connect to TP Monitor- Integration Business Logic on TP Monitor- TP Monitor Coordinates Transactions

- Client PC Write to TP Monitor Libraries

DB

UNIX

DB

TCP/IPLAN



• Late 80’s-Mid 90’s: PC Era• Client Connections to New Gen TP Monitors

• 3-Tier• Client App Uses TP Monitor API• TP Monitors Pool DB Connections• Distributed Txns Coordinated by TP Monitors• TP Monitor Acts as Integration Point for Backend Systems • Movement of Some Business Logic from Client to TP

Monitor• TP Monitors Usually Expensive



• Late 80’s-Mid 90’s: PC Era• Common Problems

• Software Distribution• Client Platform Lock-in• Limited to Business Networks



• Mid-90’s: Internet Emerges

CorporateIntranet

PC Mainframe

Tandem

ERPDB

UNIX TP MonitorsPublic

Internet

PC

Firewalls

Masses on the Internet- ISPs- Browser-Based Access- Debut of JavaISPs

Web Servers

Corporate Intranets- Firewalls- Browsers- Web Servers- Internet Access



• Mid-90’s: Internet Emerges• HTTP: Widespread, Platform-Independent Wire Protocol• HTML: Proven Very Quickly, Browser Adoption Happens Fast• Java: Applets Provide Intro for JVMs• ISPs: Provide Widespread Access Using Simple Tools• Businesses Start to Experiment with the Web

• Companies Begin to Experiment with Corporate Web Presence on Public Internet

• Still Inhibitors to Services on the Net• Security• Infrastructure Software: Web Servers Limited



• Meantime, Some Middleware Evolves• Slow Evolution, No Push Like HTML, HTTP• CORBA and Object Request Brokers (ORBs) Emerge• Message Queuing Software Emerges as Back Office

Integration Tool• ORBs Become Refined and Accepted, But Difficult to Program

Against• IIOP Isn’t Generally Accepted on the Public Internet



• Late 90’s: HTTP/HTML Spill Over Into Corporate Intranets• TCP/IP Migration of Early 90’s Sets the Stage• Driver: Admin of Clients is Very Expensive• Usefulness of HTTP/HTML and Browsers Already

Demonstrated on the Public Internet• Skilled Internet Developers Become Available• Backend Integration Starting to Become Possible via Web

Servers• CGI Programming• Servlets



Emergence of Web Application Servers


Gaining a Perspective:Emergence of Web App Servers

• Low End Approaches to Web Applications• What is a Web Application Server?• Why Did They Emerge?• How Do They Differ from…

• Web Servers?• TP Monitors?

• Transition to Application Servers



• Low End Approaches to Web Applications

Web Server Tier

Lightweight Business LogicPresentation Logic

BrowserHTML

Web ServerWeb Server

StaticContent

CGI

BrowserApplet

Servlets

JSPASP

Backend Resources

RDBMS

ExistingBusinessSystems



• Low End Approaches to Web Applications• JavaScript on Browser• Free Web Servers• Server Side Logic

• CGI• Servlets• Server Side JavaScript

• HTML Templates• ASP/IIS• JavaWebServer



• Low End Approaches to Web Applications• Limitations

• Limited Web Application Event Model• How Does One Easily Associate Button Click w/Server-

Side Business Logic?

• Lack of Robust Session Support• Beyond Cookies and URL Rewriting• Control Page Navigation• Support Session Access Across Servers




• No Easy Applet-Server Communication• Applets Using RMI or IIOP

• Must Build Server-Side Support• No Convenient Home for New Business Logic

• Limited Java Support• Might Not Want Business Logic on Web Server Tier

• Performance Considerations• Security Considerations: DMZ• Awkward to Reuse Business Logic for Non-Web Apps




• Limited Scalability/Load Distribution• Constrained by Web Server• No Sharing of Resources Amongst Web Servers• Must Rely Solely on Load Balancing in Front of Web

Server Tier

• No Easy Backend Integration• Few Tools to Ease Integration



• Role of Web Application Server

Web Server Tier

BrowserHTML

Web ServerWeb Server

BrowserApplet

Backend Resources

RDBMS

ExistingBusinessSystems

HTTP/HTTPS

IIOP

Web Application Server Tier

IIOPProxy

HTTP/HTTPS

DynamicPage

Generation

BusinessLogic

IntegrationLayer

Management

ERPSystems

CICS

TP MonitorsObject Framework



• What is a Web App Server?• Oriented Towards Interactive Web-Based Applications

• Degree of Presentation Logic and Business Logic• Place to Deploy New Business Logic

• New Point of Integration• Situated Between Web Server and Backend Systems

• Provides Backend System Access• RDBMS, TP Monitors, Business Systems

• Provides Sophisticated Session Management• Support High Availability



• Why Did Web App Servers Emerge?• TP Monitor Vendors Slow to Latch on to Web

• Not Moving at Speed of Web• Harder to Port than Java-Based App Servers

• Difficult to Build Business Apps on top of CORBA• Confluence of:

• Web-Based Apps Becoming De-facto New Model for Interactive Systems

• Hard to Program in Web Server Tier• Java JVMs Maturing, Acceptance of Java• Server Side Java Maturing• ORBs Stabilizing



• How Does an Web App Server Differ from a Web Server?• App Server Designed for Integration Role

• Meant to be a Platform for Java-Based Business Logic• Meant to Separate Presentation Logic from Business Logic

• Web Servers Designed for Serving Static Content• Dynamic Content and Heavy Business Logic is Awkward

• Web Server Not Designed for Non-HTTP• Web Server Still Has Useful Role

• Great for Static Content• Sits in DMZ: Is Accessible to Internet Clients• Good/Inexpensive for Lightweight Business Logic

• Some Web App Servers Also Serve Static HTML



• How Does a Web App Server Differ from a TP Monitor?• Hybrid of Web and Backend Integration• Supports Java/OOP• Infrastructure Typically Based on CORBA• TP Monitor is Hybrid of Old Client Server and Backend

Integration• Similarities

• Web App Servers Moving to Distributed Transactional Support

• Both Pool Connections

• Both Support Session/Context Management

• Both Oriented towards HA

• Geared Towards Enterprises



Web AppServers

EnterpriseApp

Integration(EAI)

TP Monitors

Web Cients

Request/Reply

- RPC- Messaging- Txn Coordination

- Business Systems

1999 年 5 月 shinewave international introduction to n-tier architecture

Documents

client slide

history slide

pc era slide

history timeline slide

pc era client connections

system slide

expensive slide

tier client app