CS 111

1
CS 111 Oct. 8

• Internet topics
• HTML XML
• Client / server
• Internet layers
• Commitment
• Read section 4.5.
• Quiz next Wednesday.

2
Markup languages

• HTML specifies format of Web page through ltgt and
  lt/gt commands.
• Commands convey a list of things, or are nested
  inside other commands.
• Can be generalized to all other documents
  conveying information.
• XML a general markup language that can be used
  for defining the format of any document
• One way of representing a database
• Example KML is used to define geographic
  regions for Google Earth.

3
XML example

• ltsolar_systemgt
• ltplanetgt
• ltnamegtMercurylt/namegt
• ltorbitgt88lt/orbitgt
• lt/planetgt
• ltplanetgt
• ltnamegtMarslt/namegt
• ltorbitgt687lt/orbitgt
• ltmoongt
• ltnamegtPhoboslt/namegt
• ltordergt1lt/ordergt
• lt/moongt

• ltmoongt
• ltnamegtDeimoslt/namegt
• ltordergt2lt/ordergt
• lt/moongt
• lt/planetgt
• ltplanetgt
• ltnamegtNeptunelt/namegt
• ltorbitgt60190lt/orbitgt
• // Specify 8 moons here
• lt/planetgt
• // Specify more planets here
• lt/solar_systemgt

4
Client server

• You want to perform a business transaction with a
  company via the Web.
• Internet software usually has 2 parts
• Client program Interactive Web site contains
  just enough code to get data from the user, and
  transmit it to the companys server.
• Server program Process each clients
  information.
• Why the separation?
• User (client) should not have to download entire
  program just to buy something.
• User should not log into companys computer. ?
• Server has access to huge amount of proprietary
  and confidential information.
• Many clients may want to do business at the same
  time.

5
Layers of communication

• Human layer
• Application layer client/server relationship,
  e.g. between your browser host site.
• Transport layer Your system breaks up messages
  into packets. Choose desired Internet protocol
  (TCP or UDP). Recipient assembles message.
• Network layer Routers decide best direction to
  forward packets.
• Link layer Managing the traffic, the legwork of
  moving packets.
• Each layer communicates with neighboring ones.