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Module 3 - Internet
Search Engines
Search engine anatomy
Different search engines
Effective searching techniques
Search Engines
Need for it? Multitude of web pages exist on the web. How to locate the most relevant to your needs?
Anatomy of a Search Engine Spider a.k.a robots, webbots
A program that traverses the web and stores the contents of all searchable web pages.
Web sites can deny access to some resources. Using a robots.txt file eg. Try http://www.usask.ca/robots.txt
User-agent: * Disallow: /testing
Anatomy…
Spider… Indexing Software
Indexes the web pages into a easily searchable database collection
Interface for queries Allows users to enter keywords and other combinations. Searches are performed within the indexed database
Different Search Engines www.yahoo.com
Directory listing organised into various categories Yellow pages in our phone book. All page are hand linked
“Yet Another Hierarchical Officious Oracle” Gulliver’s travels- ‘yahoo’
www.altavista.com “a view from above” First truly huge collection of indexed database of web pages
www.google.com “googol”: 1 followed by 100 zeros Top search engine today - over 100 million queries a day.
Why Google?
Relevant results are ranked at the top (first) page of a query. Why relevance is important?
Typical user rarely goes beyond the first page How is relevance measured?
Number of links that point to the same page. Not just by the number of times a keyword is repeated. Careful here: If enough people say a lie to be true, it
becomes the truth. - Goebbelsian Lies Googlebomb: “talentless hack” Googlewhack: ‘the search for the one’!!
Eg. ceremonial overstuffing
Effective Searching Composing the right keywords in the query
Saves time and frustration
AND OR NOT AND: combines two keywords
specifies that both keywords should be found on the resulting web page
OR: combines two keywords Specifies one or both keywords to be found on the web
page NOT: operates on a single keyword
Ensures that this keyword should not be found in any page returned.
Examples: vacation london OR paris bass AND fishing NOT music
Effective Searching..
+/- signs + indicates a keyword must be present in the result - indicates a keyword must not be present The signs are usually stuck to the keyword Example: +bass +fish –music
star wars episode +1
Quotation marks “ ” Groups a set of keywords and the resulting page should
have these in the exact same order Can be used in combination with other methods Examples: “star wars episode 1”
“to kill a mocking bird” -movie
Networking and Telecommunication
Topics
Linking Up: Network Basics Connecting to the Internet Networks: Near and Far Communication Software
Linking Up: Network Basics
A computer network is any system of two or more computers that are linked together.
How do networks impact systems? People share computer hardware, thus reducing
costs People share data and software programs, thus
increasing efficiency and production
Linking Up: Network Basics
Internet is a network of networks Globally connected network that links various
organisations and individuals. Web is not Internet.
WWW is one particular usage of internet. Email, FTP (File Transfer Protocol) are other such
uses.
Connecting to the Internet
The amount of information that can be transmitted in a given amount of time is defined as the bandwidth Impacted by:
Physical media that make up the network Amount of network traffic Software protocols of the network
Communication á la Modem A modem is a hardware device that
connects a computer’s serial port to a telephone line (for remote access).
Modulator-demodulator
May be internal on the system board or external modem sitting in a box linked to a serial port.
Modem transmission speed is measured in bits per second (bps) and generally transmit at 28,000 bps to 56.6K bps
Connecting to the Internet
Direct connections using T1 or T3 lines. 1.5Mpbs to 45 Mbps
Dial up connections Modems
Broadband connections DSL Digital Subscriber Line 300Kbps to 1.3Mbps Cable Modems 10Mbps.
Networks: Near and Far……
Networks Near and Far
Local-area network (LAN) Computers are linked within a
building or cluster of buildings.
Each computer and peripheral is an individual node on the network.
Nodes are connected by cables which may be either twisted pair (copper wires) or coaxial cable.
Wide-Area Networks
A network that extends over a long distance.
Each network site is a node on the WAN network Made up of LANs linked by
phone lines, microwave towers, and communication satellites.
Data is transmitted over common pathways called a backbone.
CANet3 http://www.canet3.net/stats/CAnet3map/CAnet3map.htm
CANet3: Canadian backbone
Protocols for Communication……
Communication Software
Protocol - set of rules for the exchange of data between a terminal and a computer or between two computers TCP/IP Transmission Control Protocol / Internet
Protocol Messages are broken into Packets - 1500 bytes Packets are numbered and sent over the network
Communication Software
IP defines the addressing system 128.236.24.161 - 4 bytes, 0 to 255 Every packet includes the source IP, destination
IP and the packet number (7 of 13) TCP is an end-to-end protocol.
packets are reliably transmitted from one computer to another.
Lost packets are re-transmitted.
Communication Software Communication software establishes a protocol
that is followed by the computer’s hardware Different forms:
Client/server model - one or more computers act as dedicated servers and all the remaining computers act as clients Web server and client browsers
Peer-to-peer model - every computer on the network is both client and server Napster, Gnutella
Many networks are hybrids, using features of the client/server and peer-to-peer models
Client/Server Model
Client software sends requests from the user to the server
eg. http://www.cs.usask.ca
Server software responds to client requests by providing data
Internet Addresses…
Internet Addresses
The host is named using DNS (domain name system), which translates IP addresses into a string of names. Address: 128.233.130.63 is www.cs.usask.ca Address: 216.239.51.101 is www.google.com Easier to remember strings of alphabets than
numbers.
Internet Domains
Top level domains include:
.edu - educational sites
.com - commercial sites
.gov - government sites
.mil - military sites
.net - network administration sites
.org - nonprofit organizations
.ca - Canada
Addressing Computers
Unique IP numbers Need for it? – similar to the house address
DNS servers Arranged in a hierarchy - 4 top level servers in US Multiple computers can be mapped on to the same domain
name Eg. www.yahoo.com
Gateways Takes care of routing packets in and out of a LAN
Routers Takes care of routing packets across multiple network nodes
Addressing Persons
Examples:
User President whose mail is stored on the host whitehouse in the government domain of USA
User abc123 at the server for Computer Science,University of Saskatchewan, Canada.
Internet Email Addresses
An Internet address includes: [email protected]
username is the person’s “mailbox”
hostname is the name of the host computer and is followed by one or more domains separated by periods:
– host.subdomain.domain : @mail.usask.ca
– host.domain : @hotmail.com
– host.subdom.subdom.domain : @finance.sk.gov.ca
Web Addresses
Protocol for Web pages
Dissecting Web Page address:
http:// www.vote-smart.org/
Path to the host
Resource Page
help/database.html
Addressing Resources
URL: Uniform Resource Locator Web: http://www.cs.usask.ca/index.html
A Web server stores Web pages and sends pages to client Web browsers.
FTP: ftp://ftp.cs.usask.ca File transfer protocol (FTP) allows users to download
files from remote servers to their computers and to upload files.
Telnet: telnet://scrooge.usask.ca Allows users to login into remote computers.
Other resources like Gopher, NNTP - newsgroups
Cookies
Cookies: what are they? Are files created on your computer by a website to store information about you.
To accept or not ?Benefits:
stores some of the personal information (repeat info)
allows pages to be customised to your preferences
Eg. Layouts, advertisements…
Privacy issues.
Do you want your browsing patterns to be used by a company/organisation?
Email, Viruses and Internet Issues
Topics
E-mail: Access Protocols Other Internet Applications: Chat,
Newsgroups Netiquette: some tips Intranets and Extranets Viruses Internet: Ethical and Political issues
Email on the Internet
Email formats include: ASCII text--can be viewed by any mail client program
HTML--displays text formatting, pictures, and links to Web pages
SMTP – Simple Mail Transfer Protocol Asynchronous communication form UUCP – Unix to Unix Copy
Email on the Internet
What appears on the screen depends on the type of Internet connection you have and the mail program you use.
Popular graphical email programs include Eudora, Outlook and Netscape Communicator.
Email on the Internet
IMAP Vs POP: Internet Message Access Protocol Vs Post Office
Protocol Messages remain on the email server Vs
messages are downloaded to your computer and deleted in the mail server.
Online Vs Offline access. Retrieve messages in any order Vs “in-order” retrieval Limit set by your e-mail server Vs number of
messages is limited by your hard-disk size.
Mailing Lists & Network News
Mailing lists allow you to participate in email discussion groups on special-interest topics. E-mails are sent to the whole group
A newsgroup is a public discussion on a particular subject consisting of notes written to a central Internet site and redistributed through a worldwide newsgroup network called Usenet. Protocol used NNTP – Network News Transport Protocol I-HELP is a similar application. - More like a message board. Could be local interest too: usask.forsale
Real-Time Communication
Users are logged in at the same time.
Instant Messaging for exchanging instant messages with on-line friends and co-workers
Chat Rooms for conversing with multiple people in real-time
Internet telephony (IP telephony) for long-distance toll-free telephone service
Videoconferencing for two-way meetings
Rules of Thumb: Netiquette
Say what you mean and say it with care. Keep it short and to the point. Proof-read your messages. Learn the “nonverbal” language of the Net. :) Keep your cool. Don’t be a source of spam (Internet junk mail). Lurk before you leap. Check your FAQs (Frequently Asked Questions) Give something back.
Intranets and Extranets
Intranets are self-contained intra-organizational networks that offer email, newsgroups, file transfer, Web publishing and other Internet-like services. Firewalls prevent unauthorized communication
and secure sensitive internal data Gateways where the firewalls exist, act as the
gate keeper.
Intranets and Extranets
Extranets are private TCP/IP networks designed for outside use by customers, clients and business partners of the organisation.
Electronic data interchange - EDI - a set of specifications for ordering, billing, and paying for parts and services over private networks
Viruses Viruses are programs that could damage your data
and hinder a computer’s normal functioning. Activate itself : executable files, boot sector, macros Replicate itself: through e-mail attachments Do “something”: destroy contents
Trojan horses are malicious programs disguised as useful software.
Worms are programs that could travel across the network and replicate themselves.
Anti-Virus programs check for known viruses Strains are identified by “unique” strings and their actions.
Internet Issues: Ethical and Political Dilemmas Copyright Laws: how do they apply for online
content? Especially across international boundaries.
Filtering software to combat inappropriate content Parental controls.
Digital cash to make on-line transactions easier and safer
Encryption software to prevent credit card theft Digital signatures to prevent email forgery Digital divide: computer haves from have-nots.
Next Class
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<H1>Welcome to Computer Confluence</H1><b>Publishing on the Web</b>
