Internet Basics

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Internet Basics

• Dr. Norm Friesen
• June 22, 2007

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Questions

• What is the Internet?
• What is the Web?
• How are they different?
• How do they work?
• How do they differ technically from other
  communications media (e.g. telephone)?

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The Web for Absolute Beginners (1 of 2)

• The Web is a series of documents, joined together
  by links.   These links (which can take the form
  underlined text, text labels or images) can be
  followed by simply being selected or clicked. 
  These documents can originate from almost
  anywhere in the world.
• Hypertext - a term that significantly predates
  the Web, referring to a collection of documents
  (or "nodes") containing cross-references or
  "links" which, with the aid of an interactive
  browser program, allow the reader to move easily
  from one document to another.

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The Web for Absolute Beginners (1 of 2)

• Hypermedia - The extension of hypertext to
  include other media - sound, graphics, and video
  - has been termed "hypermedia."
• Web documents - Unlike text documents, Web pages
  can be dynamic and interactive their contents
  can change in response to the reader or user's
  actions. Most dynamic Websites (www.amazon.com,
  www.blogger.com, www.cbc.ca) use information
  stored in databases to provide textual, numeric
  and other types of content for these pages.

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• A Browser - A browser (Internet Explorer, Firefox
  or another system) is the software used to view
  and interact with Web documents. 
• Client and Server - There are two basic
  categories of computers associated with the Web
  and the Internet.
• The client computer is used to view Web pages
  with a browser and an Internet connection of some
  kind.   When you (or your students) access WebCT
  from home, office, a computer lab, or a
  classroom, you will be using a client computer.  

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• The server computer stores Web documents and
  "serves" their contents across the Web.  Server
  computers can be located anywhere in the world,
  but must be connected to the Web using a
  permanent, high-speed link.
• Software that makes Websites interactive and
  dynamic is generally located on the server.  It
  generally involves a database. This means that
  for most types of Web-based interactivity, a
  standard Web browser is sufficient.

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• Protocol specific rules for accessing and
  transmitting data. Different protocols (e.g.
  "http" or "shttp") are used for different kinds
  of information. (often includes errors)
• URL or Web Address a combination of characters
  (letters, numbers, punctuation) that is unique on
  the Web, and that indicates the specific location
  of a file or resource on a particular server.

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Addresses

• Flash Java Applets are examples of technologies
  that provide interactivity by being downloaded to
  and operating on the client computer.
• Document Locations or Web Addresses
• Each page or document on the Web has a unique
  address.   This address identifies every
  important element involved in accessing the
  document, including
• the protocol or set of technical rules used to
  transmit the document
• the organization providing the server that hosts
  the document on the Web
• the nature or nationality of the organization
• the part of the server accessed (port number)
• the computer directories or folders in which the
  Web page is stored (optional)
• the name of the Web page file  

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"Layers"

• Computer and network systems are designed in
  terms of clearly separated but independent
  components.
• In a network, these are referred to as "layers"
  (can be divided in different ways)
• Physical the actual wire or fibre on which
  information is transmitted can be phone line
• Application
• Content

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Websites

• sub-site structure often contains the real
  "content" of the web site often uses a
  nonhierarchical organizational logic
• linear most common format useful for documents
• listing or index (usually alphabetical) useful
  for links or alternative organization of larger
  sites
• grid useful for large, uniform information sets,
  like an expanded table. Can be combined with a
  hierarchy.
• database for searches on large information sets.
  Requires special server software.

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• Databases on the Web An important example of
  Internet/PC Architecture
• To make the contents of a database accessible
  over the Web, it is necessary to make use of
  special software that resides on a server.
  Special software forms the middle component or
  tier in what is commonly known as a three-tier
  system. This simple "stack" architecture is
  comprised of
• Database Tier the data or database file residing
  on the server. Also known as the database server.
• Middle Tier database connectivity software
  making the database securely available on the
  web.
• Client Tier the client or browser used to search
  and modify database records.

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• data is passed back and forth between these tiers
  or components, basically in the form of search
  requests and results.
• The middle tier acts as an interpreter,
  translating information into the different
  languages or protocols understood by the browser
  and database.
• It receives a query from a web page form, coded
  in a web protocol.
• It translates this query into a simple but
  powerful Structured Query Language (SQL)
  statement, which can be understood by almost any
  type of database.
• the connectivity software receives the results
  from the database as pieces of text that it must
  then format as a web document using HTML
  (HyperText Markup Language).

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TCP/IP Protocols

• The internet as a postal system, not a telephone
  system.
• Why?

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Cold War and the Internet

• One central "hub" makes the entire network
  vulnerable
• Many "hubs" means that the network can operate
  even if one or more ceases to exist.
• DARPA Defense Advanced Research Projects Agency

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