Client Server and Internet

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• Client /Server and Internet
• Lecture 4

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OVERVIEW

• Web Technology
• The Interactive Web
• Common Gateway Interface (CGI)
• Web Client/Server (Java Style)

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Web Technology

• Four technologies on top of the Internet
  infrastructure
• URL (Uniform Resource Locator) used to globally
  name and access all Web resources.
• HTTP used to access and retrieve URL-named
  resources.
• HTML used to embed hyperlinks and to describe
  the logical structure of Web documents.
• Web browser used as universal client.

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Static, Read-only HTML Pages
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Dynamic, Interactive Web Server (3-tier
Architecture)
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1
4
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http
//www.address.com
7800
/path/subdir/file.ext
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Client-side Technology

• HTML
• JavaScript
• Visual Basic Script
• Java Applet
• ASP.NET Client-Side Scripting

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Common Gateway Interface (CGI)

• CGI is the method that Web servers use to
  communicate with programs that Web developers
  write to respond to user input from the Web.
• CGI is language independent.
• CGI programs reside on the same machine as the
  Web server.

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Calling a CGI Script using a Form
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Interacting with forms
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CGI AND STATE

• Hidden Fields are basically invisible they
  contain values that are not displayed within a
  form
• Cookies is a small piece of data that is stored
  in the client on behalf of a server.

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Cookies

• Cookies is a small piece of data that is stored
  in the client on behalf of a server.
• A server can put any text value in the cookie
  response header field
• The client can store the cookie value on
  secondary storage for later use
• When requesting another page from the same
  server, the cookie value is included in the HTTP
  request's cookie header field
• The server can maintain an administration of
  cookie values to simulate state across HTTP
  transaction boundaries

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Web Client/Server , Java-Style

• Java Applet

• Request the applet.
• Receive the applet.
• Load and execute the applet.
• Discard the applet.

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Web Client/Server , Java-Style

• Java Servlets

• All java plug-in for servers
• CGI replacement but remains in memory after a
  client request
• Servlets can retain connnections to a database
• Servlets can make calls to other servlets
• Good for processing user input

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Resource Tutorial

• Server-side scripting technology for creating
  dynamic and interactive web applications
• ASP
• http//msdn.microsoft.com/workshop/server/asp/a
  sptutorial.asp
• JSP
• http//developer.java.sun.com/developer/onlinetr
  aining/jspintro/
• Server-side application technology
• Servlet http//java.sun.com/docs/books/tutorial/s
  ervlets/TOC.html
• Perl
• http//archive.ncsa.uiuc.edu/General/Training/Pe
  rlIntro/

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