Creating Web Documents: How the Web works

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Creating Web Documents How the Web works

• Client / Server
• Protocols
• Access methods
• Homework Complete experiment report on
  Discussion Forum

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How the web works

• Client/server server, holding information
  receives requests from client (you/your browser).
  Typical request is for a file
• Protocols rules to be followed by different
  computer programs. Many protocols are involved.
• Transmission Control Protocol/Internet Protocol
  controls transmission of packets (files divided
  into smaller pieces) and routing to the address.
  Uniform Resource Locator indicates which protocol
  (e.g., http//, ftp, mailto) and which server
  address (domain name possibly followed by
  directories file names
• Route of packets can vary, so transmission needs
  to be reassembled at each end.

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tracert

• Route from one point to another can be many steps
  and can vary.
• This redundancy is basic characteristic of the
  Web
• On Windows machine, click on Start/Run/ to get
  command prompt type in command if not present
• After gt type in tracert URL
• gttracert www.nytimes.com

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How the web works, cont.

• Hypertext Transfer Protocol
• Client opens the connection, at URL and at port
• Client makes a request
• Server sends response
• Connection closed
• An HTML file with 2 images requires 3
  connections. No information kept between
  connections stateless system

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cache

• More complex
• Files are stored in what is called the cache.
• Maybe local cache and network cache.
• Browser 'looks around' to see if there is already
  a copy of the file requested.
• May send a message to check on time to see if
  this file has been updated.
• Generally works BUT sometimes, you may need to
  exit and re-invoke browser or even clear out
  cache to get latest version.

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Server side programming

• Programs (scripts) run on server to handle
  databases, files, other computations.
• Use common gateway interface (cgi).
• You may read about cgi/perl programs
• Newer middleware systems asp, php, cold fusion
• Topic of Creating Databases for Web Applications
  course.
• When server gets request for a file of type pl,
  php, asp, cf, it executes the file instead of
  returning it as is to the browser.
• These programs create HTML file dynamically,
  possibly using information stored on server.

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Connections

• Dial-up phone service. A modem changes the
  computer (digital signal) to electronic and a
  modem at other end changes electronic back to
  digital.
• Faster connections are referred to as broadband
• DSL (digital subscriber line) a technology that
  exploits unused frequencies on copper telephone
  lines to transmit traffic typically at
  multi-megabit speeds. DSL can allow voice and
  high-speed data to be sent simultaneously over
  the same line. Because the service is 'always
  available,' end-users don't need to dial in or
  wait for call set-up.
• Cable modem uses the cable line.

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Browser

• Interprets the HTML document
• Displays the text
• Tags set up action for what is between the tags
• Image files and other media are displayed by
  browser itself or by call to a helper/plugin
  program
• The a tag (and tags for forms) set up new
  requests to servers.

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Other browsers

• Personal Digital Assistants (PDAs) and cell
  phones have special and distinct browsers.
• Wireless Application Protocol (WAP) enabled
  phones are an example. These browsers work with
  slower connections, less storage space.
• Also refer to WAP enabled sites sites
  specialized for use by WAP phones. Use Wireless
  Markup Language and Wmlscript.
• One of several topics in Creating User
  Interfaces.
• IF YOU HAVE such a phone, use it for the
  experiment!

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Uploading projects to our web site

• File management
• Multiple files for web page
• For now, keep each project in one directory
• Make name of main HTML file (probably only have
  one) index.html
• Keep names simple lower case, no spaces
• Critical if server operating system not the one
  you are using for development
• Ws-ftp (file transfer protocol)

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The lta href.gt

• Link to (external) web site
• hrefhttp//.....
• Link to html file on same server, same folder
• href"filename.html"
• Link to html file on same server, in parent
  folder
• href"../filename.html"
• Link to place in same file
• href"place"
• lta name"place"gt

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Assignment

• Pick 2-3 Web sites and view them in different
  ways (PC vs Mac vs cell phone vs WebTV, IE vs
  Netscape vs Opera vs AOL, Campus network
  (Ethernet to shared T1) vs business network
  (network to T1/T3) vs phone modem vs DSL vs cable
  modem, ???)
• Report on experience to appropriate Forum on
  CourseInfo. Comment on layout, colors, speed,
  anything else.