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Distributed Information Systems - The Client server model Week 1 – Lecture 2
Client server model <ul><li>Any computer connected to a network is called a  host  –  ( a host for a process which provide...
Operating system Proc A  Proc B Proc C Operating system Proc X  Proc Y Proc Z Client process Client process Server process...
A brief history of IS 1970’s 1980’s 1990’s 2000’s Main frame or mini with dumb terminals LAN server & PC s 2 tier Client S...
Application layers <ul><li>Presentation </li></ul><ul><ul><li>Formatting & displaying data </li></ul></ul><ul><ul><li>Disp...
Network Dumb terminals Centralised Mainframe or Minicomputer Basic presentation Form definition Application Database File ...
Centralised mainframe or Mini computer <ul><li>Weaknesses </li></ul><ul><ul><li>Constrained by single server </li></ul></u...
Network PCs PC Lan PC Server File system Presentation Application Database
Network PCs PC Lan File Server Operating system Application Operating system File system
PC LAN <ul><li>Weaknesses </li></ul><ul><ul><li>Very high bandwidth – LAN only </li></ul></ul><ul><ul><li>Constrained by s...
Network PCs 2 Tier Client server Database Server PC or UNIX Database File system Presentation Application
Network PCs 2 Tier Client server Database Server Windows or UNIX Proc C Operating system File system Operating system Appl...
Two Tier Client Server <ul><li>Weaknesses </li></ul><ul><ul><li>Constrained by single server </li></ul></ul><ul><ul><li>Di...
Network PCs Servers Database File system Presentation 3 Tier Client/Server Application
Network PCs 3 Tier Client/Server Proc C Operating system File system Operating system Presentation Process Database Proces...
Three Tier Client Server <ul><li>Weaknesses </li></ul><ul><ul><li>Presentation layer still distributed </li></ul></ul><ul>...
Network PCs Servers Database File system Browser 4 Tier Client/Server Application Web
Network PCs 4 Tier Client/Server Proc C Operating system Browser Process Proc C Operating system Application Process Opera...
Four Tier Client Server <ul><li>Weaknesses </li></ul><ul><ul><li>Browser not designed for TP </li></ul></ul><ul><ul><li>Pe...
 
The Advantages of distribution <ul><li>Scalable </li></ul><ul><ul><li>Additional servers can be added as needed </li></ul>...
The advantages of being centralised <ul><li>Architecturally simpler </li></ul><ul><li>All software and hardware from one s...
Communications & Networks <ul><li>How does the client host find the server host ? </li></ul><ul><li>Having found the serve...
Distributed Components <ul><li>How does the client know what server can perform the service? </li></ul><ul><li>What format...
Integrating disparate systems <ul><li>Organisations have many separate systems </li></ul><ul><li>Systems in one organisati...
Security <ul><li>How do we prevent unauthorised users accessing the system? </li></ul><ul><li>How do we prevent authorised...
Server platform <ul><li>There are many different operating systems, computer suppliers, types of middleware etc </li></ul>...
Performance, scalability & reliability <ul><li>Most DIS have many concurrent users </li></ul><ul><li>How do we design a sy...
International differences <ul><li>Users often come from many different countries </li></ul><ul><li>How does the system ada...
Case study <ul><li>Rory Collins – ex CIO of the ASX </li></ul><ul><li>Will discuss a major project to implement a new syst...
Next week <ul><li>Basic concepts in computers communicating with each other. </li></ul>
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Slides for Week 1 - Lec 2

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Slides for Week 1 - Lec 2

  1. 1. Distributed Information Systems - The Client server model Week 1 – Lecture 2
  2. 2. Client server model <ul><li>Any computer connected to a network is called a host – ( a host for a process which provides or requests a service ) </li></ul><ul><li>The process on a client host requests a service from a process on the server host </li></ul><ul><li>A process is a program running within a host </li></ul>
  3. 3. Operating system Proc A Proc B Proc C Operating system Proc X Proc Y Proc Z Client process Client process Server process Server process Host 1 Host 2 Proc. A asks Proc. X to Perform a service. Proc. Z asks Proc. C to Perform a service Host 1 does not ask Host 2 to perform a Service
  4. 4. A brief history of IS 1970’s 1980’s 1990’s 2000’s Main frame or mini with dumb terminals LAN server & PC s 2 tier Client Server 3 & 4 tier Client server
  5. 5. Application layers <ul><li>Presentation </li></ul><ul><ul><li>Formatting & displaying data </li></ul></ul><ul><ul><li>Displaying a form & accepting data </li></ul></ul><ul><ul><li>Checking the validity of the data entered </li></ul></ul><ul><li>Application – the business logic </li></ul><ul><li>Database – storing and locating data </li></ul><ul><li>File system - recording and reading records on disk </li></ul>
  6. 6. Network Dumb terminals Centralised Mainframe or Minicomputer Basic presentation Form definition Application Database File system
  7. 7. Centralised mainframe or Mini computer <ul><li>Weaknesses </li></ul><ul><ul><li>Constrained by single server </li></ul></ul><ul><ul><li>Expensive hardware at the time </li></ul></ul><ul><li>Strengths </li></ul><ul><ul><li>Low bandwidth network </li></ul></ul><ul><ul><li>Architecturally simple </li></ul></ul><ul><ul><li>Most hardware & system software from the one supplier </li></ul></ul>
  8. 8. Network PCs PC Lan PC Server File system Presentation Application Database
  9. 9. Network PCs PC Lan File Server Operating system Application Operating system File system
  10. 10. PC LAN <ul><li>Weaknesses </li></ul><ul><ul><li>Very high bandwidth – LAN only </li></ul></ul><ul><ul><li>Constrained by single server </li></ul></ul><ul><ul><li>Software is distributed </li></ul></ul><ul><li>Strengths </li></ul><ul><ul><li>Cheap hardware </li></ul></ul><ul><ul><li>Provides low cost systems to small organisations with up to 20 users </li></ul></ul>
  11. 11. Network PCs 2 Tier Client server Database Server PC or UNIX Database File system Presentation Application
  12. 12. Network PCs 2 Tier Client server Database Server Windows or UNIX Proc C Operating system File system Operating system Application Database
  13. 13. Two Tier Client Server <ul><li>Weaknesses </li></ul><ul><ul><li>Constrained by single server </li></ul></ul><ul><ul><li>Distributed software </li></ul></ul><ul><ul><li>Not scalable </li></ul></ul><ul><li>Strengths </li></ul><ul><ul><li>Relatively simple architecture </li></ul></ul><ul><ul><li>Cheap hardware </li></ul></ul>
  14. 14. Network PCs Servers Database File system Presentation 3 Tier Client/Server Application
  15. 15. Network PCs 3 Tier Client/Server Proc C Operating system File system Operating system Presentation Process Database Process Proc C Operating system Application Process
  16. 16. Three Tier Client Server <ul><li>Weaknesses </li></ul><ul><ul><li>Presentation layer still distributed </li></ul></ul><ul><ul><li>Complex architecture </li></ul></ul><ul><li>Strengths </li></ul><ul><ul><li>Scalable </li></ul></ul><ul><ul><li>Consistent Performance </li></ul></ul><ul><ul><li>Lower bandwidth than 4 tier </li></ul></ul>
  17. 17. Network PCs Servers Database File system Browser 4 Tier Client/Server Application Web
  18. 18. Network PCs 4 Tier Client/Server Proc C Operating system Browser Process Proc C Operating system Application Process Operating system File system Database Process Operating system WEB Server
  19. 19. Four Tier Client Server <ul><li>Weaknesses </li></ul><ul><ul><li>Browser not designed for TP </li></ul></ul><ul><ul><li>Perhaps higher bandwidth than 3 tier </li></ul></ul><ul><ul><li>Complex architecture </li></ul></ul><ul><li>Strengths </li></ul><ul><ul><li>Software not distributed </li></ul></ul><ul><ul><li>Scalable </li></ul></ul>
  20. 21. The Advantages of distribution <ul><li>Scalable </li></ul><ul><ul><li>Additional servers can be added as needed </li></ul></ul><ul><li>Open </li></ul><ul><ul><li>Software components can be replaced or added </li></ul></ul><ul><li>Heterogenous </li></ul><ul><ul><li>Software can be in different languages, need different operating systems, run on different hardware </li></ul></ul><ul><li>Fault tolerant </li></ul><ul><ul><li>While multiple servers is inherently more likely to result in errors, they also provide redundancy </li></ul></ul>
  21. 22. The advantages of being centralised <ul><li>Architecturally simpler </li></ul><ul><li>All software and hardware from one supplier </li></ul><ul><li>Eliminates the overhead of distribution </li></ul><ul><li>Easier to control security </li></ul><ul><li>On average, requires less bandwidth </li></ul>
  22. 23. Communications & Networks <ul><li>How does the client host find the server host ? </li></ul><ul><li>Having found the server host, how are messages reliably passed between them, over telephone lines, wireless links, optical fibre cables? </li></ul><ul><li>This is the subject matter of communications and networks </li></ul><ul><li>(weeks 2-5) </li></ul>
  23. 24. Distributed Components <ul><li>How does the client know what server can perform the service? </li></ul><ul><li>What format does the client use to pass the parameters to the server? </li></ul><ul><li>Week 6 </li></ul>
  24. 25. Integrating disparate systems <ul><li>Organisations have many separate systems </li></ul><ul><li>Systems in one organisation have to integrate with systems in another </li></ul><ul><li>Systems are usually developed in complete isolation from each other – often many years apart. </li></ul><ul><li>They use different data definitions, different coding structures, different data values </li></ul><ul><li>These systems still have to work together. </li></ul><ul><li>Week 7 - 9 </li></ul>
  25. 26. Security <ul><li>How do we prevent unauthorised users accessing the system? </li></ul><ul><li>How do we prevent authorised users doing things they should not, or seeing data they must not? </li></ul><ul><li>How do we identify and authenticate a user? </li></ul><ul><li>How do we pass messages between systems without those messages being intercepted? </li></ul><ul><li>Week 10 </li></ul>
  26. 27. Server platform <ul><li>There are many different operating systems, computer suppliers, types of middleware etc </li></ul><ul><li>What are the critical differences? </li></ul><ul><li>How do we select the right software and hardware to meet our system needs? </li></ul><ul><li>Week 11 </li></ul>
  27. 28. Performance, scalability & reliability <ul><li>Most DIS have many concurrent users </li></ul><ul><li>How do we design a system to give the required level of performance </li></ul><ul><li>The number of users and the quantity of data will increase, how do we add hardware and change the software to accommodate those extra users and maintain the required levels of performance & reliability? </li></ul><ul><li>(week 11) </li></ul>
  28. 29. International differences <ul><li>Users often come from many different countries </li></ul><ul><li>How does the system adapt to the specific needs of each user </li></ul><ul><ul><li>Language </li></ul></ul><ul><ul><li>Character set </li></ul></ul><ul><ul><li>Legal system </li></ul></ul><ul><ul><li>Tax laws </li></ul></ul><ul><ul><li>Currency </li></ul></ul><ul><li>Week 12 </li></ul>
  29. 30. Case study <ul><li>Rory Collins – ex CIO of the ASX </li></ul><ul><li>Will discuss a major project to implement a new system for the Singapore Stock Exchange </li></ul><ul><li>Week 12 </li></ul>
  30. 31. Next week <ul><li>Basic concepts in computers communicating with each other. </li></ul>

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