Web Applications

1
Web Applications

• Charles Song
• Feb 16 2006

2
Web Server

• A piece of software
• Listens for HTTP requests
• Sends back HTTP responses

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Web Server

• Apache HTTP Server
• Internet Information Services (IIS)
• Sun ONE Web Server

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Web Server

• Serves up contents (html, images, txt)
• Static contents
• Dynamic contents

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Static Contents

• HTTP request comes in
• Sends existing html file back
• ttp//www.server.com/dir1/file1.html
• ltserver root dirgt/dir1/file1.html

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Dynamic Contents

• HTTP request comes in
• Generates HTML page
• Sends generated HTML back

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Dynamic Contents

• CS Forum for CMSC 498W
• ttp//forum.cs.umd.edu/forumdisplay.php?f17
• Magic!!!

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Pros

• Static Contents
• Faster responses
• Less CPU usage
• Dynamic Contents
• Less file management
• Easier to update contents

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Web Applications

• A web application is an application delivered to
  users from a web server over a network such as
  the Internet or an intranet. wikipedia

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Advantages

• Only needs a web browser to use the application
  (Thin Client)
• Easy to distribute and update application

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Web Application Examples

• Webmail (gmail)
• Forums (CS Forum)
• Wikis (wikipedia)
• Weblogs aka blogs (blogger)

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Three-Tiered Architecture

• Web Browser
• Dynamic Content Engine
• Database

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First Tier Web Browser

• Sends Requests to middle tier
• ttp//www.amazon.com/index.jsp?item5
• Displays HTML responses

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Second Tier Dynamic Content Engine

• Processes requests
• ttp//ww.amazon.com/index.jsp?item5
• Runs index.jsp with parameter item 5
• Makes queries to the database
• Generates HTML with information from database
• Sends back response

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Third Tier - Database

• Stores data
• e.g. Amazon.coms database stores
• Items for sale
• Customer information

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Dynamic Content Engines

• Java Server Pages (JSP) and Servlets
• Active Server Pages (ASP)
• PHP
• CGI

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Technology Stacks

• L.A.M.P.
• Linux Operating System
• Apache HTTP Server
• MySQL Database
• PHP, Python or Perl Scripting Language
• J2EE
• .NET

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Server Side Caching

• Reduces web server load
• Faster response time
• Saves recently or frequently accessed resources
• file system
• memory

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URL Tricks

• ttp//www.blog.com/a_user/a_blog
• Middle tier knows to parse out a_user and a_blog
• Queries database with parameter user a_user and
  blog a_blog
• ttp//www.blog.com/?user_userblog_blog
• ttp//www.blog.com/post/174367.html
• Queries database for posts with id 174367
• ttp//www.blog.com/?typeostid174367

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URL Tricks

• Motivations
• Search engine indexing
• Easier to remember
• Prettier URL ?

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Wiki

• a type of ebsite that allows users to easily add
  and edit content and is especially suited for
  ollaborative writing - wikipedia

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Wiki Editing

• Use of Wiki syntax
• User-editable (easier than html)
• Render HTML from Wiki syntax
• Who should have access to edit?

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Wiki Usage

• Encyclopedia (wikipedia)
• Books
• Business Projects

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Blog

• a ebsite that allows authors to post items on a
  regular basis and usually displayed in reverse
  chronological order.

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Blog Usage

• Personal Diary
• News
• Business Projects