1. 1999 年 5 月 Shinewave International Introduction to N-Tier Architecture

2. 1999 年 5 月 Shinewave International 3-tier 架構 (Presentation,Logic,DB Access) Application (Browser) ActiveX Control Client Site (UI/Win95) Application Server DB Server Middle Site (MTS/NT) Server Site (SQL/NT) Server Application

3. 1999 年 5 月 Shinewave International N-tier 示意圖 Browser Web Load Balance Browser Web Server Web Server Web Server AP Server AP Server AP Server AP Server Message Queue DB Server Other System

4. 1999 年 5 月 Shinewave International 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

5. 1999 年 5 月 Shinewave International Gaining a Perspective A Bit of History

6. 1999 年 5 月 Shinewave International 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

7. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History Timeline

8. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 70’s-80’s: Age of the Green Screen

9. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 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

10. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History Late 80’s-Mid 90’s: PC Era

11. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 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

12. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 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

13. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History Late 80’s-Mid 90’s: PC Era Client Connections to New Generation TP Monitors

14. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 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

15. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History Late 80’s-Mid 90’s: PC Era Common Problems Software Distribution Client Platform Lock-in Limited to Business Networks

16. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History Mid-90’s: Internet Emerges

17. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 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

18. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 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

19. 1999 年 5 月 Shinewave International Gaining a Perspective: Bit of History 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

20. 1999 年 5 月 Shinewave International Gaining a Perspective Emergence of Web Application Servers

21. 1999 年 5 月 Shinewave International 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

22. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers Low End Approaches to Web Applications

23. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers 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

24. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers 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

25. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers Low End Approaches to Web Applications Limitations 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

26. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers Low End Approaches to Web Applications Limitations 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

27. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers Role of Web Application Server

28. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers 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

29. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers 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

30. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers 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

31. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers 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

32. 1999 年 5 月 Shinewave International Gaining a Perspective: Emergence of Web App Servers