Introduction to Networks

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Introduction to Networks
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Data Communications Network
A collection of computer systems configured to
share digital data and resources
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Local Area Networks

• LANs extend across limited geographical area
• servers, terminals, etc.

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Internetwork

• collection of autonomous networks
• The Internet
• Network spanning the world
• intranets
• single organization (ie Malu)

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The Internet

• Developed by the US Dept of Defence in the 60s
  as a link to the missile silos of North Dakota.
• The network had to be
• Decentralized no single, central, managing
  authority.
• Loosely-coupled can continue communication even
  if parts of the system fail since components are
  autonomous.
• Redundant the network contains many paths
  between any two components.

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Internet Applications

• e-mail
• telnet
• ftp (file transfer protocol)
• World Wide Web

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World Wide Web

• created as a medium for disseminating scientific
  research
• organized by Tim Berners-Lee in 1989
• hypertext system
• Documents with built-in cross-referencing called
  hyperlinks
• open system since anyone may link into the web

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Client/Server

• CLIENT--(local) system requesting services
• SERVER--(remote) system that receives and
  handles requests from many clients concurrently
• P2P a computer may be both a client and server,
  WinMX, Kazaa

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Web as Client/Server App

• Protocol--a set of rules that govern how an
  activity takes place
• HTTP--(HyperText Transfer Protocol) specifies how
  Web clients and servers communicate
• URL--(Uniform Resource Locator) addressing for
  Web resources
• HTML--(HyperText Markup Language) defines content
  and display of Web pages

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Anatomy of a URL
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Search Engines

• What are you really searching?
• Finding the web documents (Web pages or
  sites) you want can range from extremely easy
  to impossible.
• This is due to the size of the Web - currently
  estimated at approx. 1 billion documents.
• There is also no standard cataloging system in
  place.
• When you are searching the Web you are not
  searching it directly. You are actually querying
  an intermediate database which will supply you
  with the URLs of other pages.
• How is this database built?

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Researching on the Web

• The two main categories of search tools are
• Subject or Web directory --a search service
  organized as a topical hierarchy and compiled by
  (human) editors. (ie Yahoo, about.com, etc)
• Search engine--search services whose databases
  are compiled by automated Web crawlers. (ie
  Google, Alta Vista, InfoSeek, etc.)

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Search Engines

• Search by keyword, trying to match exactly the
  words in the pages to those in the criteria set
  up by the user.
• No browsing, no subject categories
• Databases are compiled by "spiders"
  (computer-robot programs) with minimal human
  contact
• Search-Engine size from small and specialized to
  90 percent of the indexable Web
• Good search engines
• Google, MSN Search, AltaVista, Lycos

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Keyword Searching

• A form of (automated) text matching
• keyword--a word or phrase used as a text pattern
  for matching
• hits--matches with text patterns
• misses--fails to match some or all of the text
  pattern
• false positives--hits that are not related to the
  desired topic (ie Ford cars not president)

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Hybrid Search Services

• metasearch engines--consult other search engines
  and directories and summarize query.
• niche services--commercial services targeted at a
  specific audience or topic.
• Kellys blue book for used cars
• portals--gateway Web site with searching
  capabilities (ie Yahoo, Excite, NBCi.com)

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Meta-Search Engines

• Meta-Search Engines quickly and superficially
  search several individual search engines at once
  and return results compiled into a sometimes
  convenient format.
• Examples of Meta-Search engines Metacrawler,
  Inference Find, Ixquick
• Problems with meta-search engines
• only spend a short time in each database (cover
  only about 10)
• meta-searchers simply pass your search terms
  along
• They omit some good, large search engines.

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Choosing Effective Keywords

• Five to ten keywords are better than one or two
• Names of specific people and places help
  capitalize
• Only capitalize proper names (first letter only)
• Include the name of an organization that may post
  the info you seek
• Use specific nouns that are relevant to your
  topic
• Include alternative spellings or abbreviations of
  important names
• Play with variations on your query
• Use truncation and wildcards () (ie color)
• If a keyword seems to mislead the search engine
  delete it
• Put more important keywords first

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Subject Directory

• Is a hierarchically organized collection of
  categories and subcategories that can be browsed
  to locate specific information.
• Are created and maintained by human editors who
  review and select sites for inclusion in their
  directories on the basis of previously determined
  selection criteria.
• When browsing, always start at the top of the
  directory.
• Usually you use subject trees for mainstream type
  data.
• There are different types of subject directories
  general directories, academic directories,
  commercial directories.

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Search Tool Features

• Phrase Searching is a feature you want in every
  search tool you choose.
• Requires your terms all to appear in exactly the
  order you enter them.
• Enclose the phrase in double quotations " "
• Examples
• "affirmative action" , "world health
  organization" , "Bill Gates"
• Boolean operators
• AND
• The AND operator makes sure all the terms you
  request appear on the selected sites. If you type
  Java AND JavaSoft your search will return pages
  about the Web's programming language, not coffee.
  
• Nearly the same effect comes with the sign
  which forces all terms to be in all documents
  retrieved.
• I.e. Java JavaSoft

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Search Tools Features - cont.

• OR
• Use OR to return pages that contain either of two
  terms. For example, Microsoft OR Netscape
• Best to us parenthesis with OR ie (Microsoft OR
  Netscape)
• NOT
• Use NOT to ensure that certain words won't appear
  in your search selections. Modems NOT internal.
• BOOLEAN AND NOT helps narrow searches
• "biomedical engineering" AND cancer AND NOT
  "Department of" AND NOT "School of"
• - gives the same result
• "biomedical engineering" cancer -"Department
  of" -"School of
• Always capitalize logical and Boolean operators

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Search Tools Features - cont.

• Parentheses
• Organize your searches even further by using
  parentheses.
• NOT Malaspina AND Cooke will return pages with
  Cooke in them
• NOT (Malaspina AND Cooke) will avoid pages with
  both names.
• Put most important keywords first in the search
  string.
• Italian (vineyards or vines)
• Always check your search engine for Boolean
  requirements. AND NOT vs ANDNOT etc
• Field, Title, Domain, and Host searching

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Subject-Specific Databases

• Subject-Specific Databases are databases devoted
  to a single subject, created by researchers,
  experts, government agencies, and/or other
  individuals with a specialized interest or
  accumulated info on a subject.
• Examples
• ERIC Clearinghouses
• Expedia (travel)
• Kelley Blue Book
• MySimon (comparison shopping)
• SportSearch
• WebMD

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E-Commerce

• E-Commerce is rapidly emerging as an essential
  business strategy
• Being driven by customer expectations from
  traditional business model
• E-Commerce has the following components
• Web interface on the client side
• backend databases on the server side
• scripts to enable the interaction of these two

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Client-Side Scripting in E-Commerce

• Resides on the client machine (downloaded with
  the Web interface)
• Creates client interactivity
• Collects data from the user
• Does preliminary analysis and validation on
  user-supplied data
• Sends validated data to the server

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Server-Side Scripting in E-Commerce

• Resides on the server
• Accepts data from the client
• Uses that data to
• search backend databases
• write to databases
• initiate credit card processes, etc.
• Returns response data to the client

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Client-Side Processing with HTML

• Web pages are cross-platform documents they may
  be viewed on any computer provided it has an
  appropriate browser installed.
• Web pages have become the default standard for
  creating and publishing documents electronically.
• WWW documents are written in the language HTML in
  which HTML Hypertext Markup Language

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Web Document Characteristics

• They are constructed to be resolution
  independent.
• May contain text, sounds, images, graphics and
  video clips.
• Are hypertext documents in that they contain
  electronic links to other web published
  information.
• HTML is designed to implement these
  characteristics.

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HTML Characteristics

• Read Pages 92 101 Digital Domain
• HTML allows us to define separately both the
  content and presentation of a document.
• Once the document has been defined in HTML it is
  stored on a web server. When a client browser
  accesses the server and requests this document it
  is transferred to the client browser. The client
  browser then interprets the structure and
  displays it. The user of course may set browser
  preferences.

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HTML document

• HTML documents consist of marked-up plain (or
  unformatted) text, with special embedded markings
  to tell the browser how the text is to be
  displayed.
• HTML code is just plain text with markup codes
  (called tags) interspersed in it.
• The HTML code is saved as a plaintext file with
  .html or .htm extension to indicate the file
  type.

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HTML document

• paired tags
• lttag_idgtcontent affected by taglt/tag_idgt
• standalone tags
• lttag_idgtcontent after the tag
• Metatags are special descriptions stored in the
  HTML file which among other things help search
  engines build their databases.

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HTML Document Structure
lt!DOCTYPEgt lthtmlgt ltheadgt lttitlegtdescription of
the pagelt/titlegt ltmeta namemetaname
contentmetacontentgt other head
elements lt/headgt ltbodygt body elements go
here lt/bodygt lt/htmlgt
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Web Publishing Applications

• General editor e.g. Notepad
• tag editors
• help with editing HTML code
• e.g., CoffeeCup
• HTML generators (editors)
• WYSIWYG design views
• e.g., Macromedia Dreamweaver, FrontPage

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Client-Side Processing and DHTML

• Dynamic HTML (DHTML) is
• a collection of technologies to make client-side
  interactions better and more interactive
• is a bit of a misnomer it is not an extension
  of HTML
• DHTML is not standardized
• different browser companies compete with their
  own DHTML features
• as long as the browser wars persist, DHTML is
  unlikely to be standardized
• Two important components of DHTML
• CSS (cascading style sheets)
• client-side scripting

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Cascading Style Sheets (CSS)

• Define styles for formatting and displaying
  information
• provides for better Web site internal consistency
• makes Web site style modifications much easier
• Three types of CSS
• inline
• embedded
• external
• applied with precedence inline-gtembedded-gtexterna
  l

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Client-Side Scripting and Forms

• Scripting works hand-in-hand with HTML forms
• HTML forms have built-in mechanisms for
  soliciting and collecting user data
• Forms are a part of standard HTML
• Client-side scripts are used to take action on
  the data collected before sending it to the
  server
• Such scripts are invoked using the onSubmit event
  handler
• Other events could be onMouseOver, OnClick

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Server-Side Scripting

• Accepts data from client
• Often written in
• CGI (Common Gateway Interface)
• actually an interface rather than a scripting
  language
• can be written in a number of different scripting
  languages
• PHP HyperText Preprocessor
• ASP (Active Server Pages Microsoft)

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Java Programming

• Java is an object-oriented full-purpose (as
  opposed to scripting only) programming language
• Java is noted for its excellent cross-platform
  capability
• Java applets are small Java programs designed
  specially for the Web to be downloaded and run on
  a client machine.