Chapter 16: The World Wide Web

Chapter 16: The World Wide Chapter 16: The World Wide WebWeb

Chapter 16Chapter 16The World The World Wide WebWide Web

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Click on this piece Click on this piece of hypertext, and of hypertext, and you’re taken to...you’re taken to...

Type in a keyword Type in a keyword and click the “Go!” and click the “Go!”

pushbutton, and pushbutton, and you’re taken to...you’re taken to...Click on this Click on this

pushbutton, and pushbutton, and you’re taken to...you’re taken to...

The World Wide Web applies The World Wide Web applies point-and-click point-and-click hypermediahypermedia application software to application software to facilitate accessing facilitate accessing documents on the Internet via documents on the Internet via TCP-based protocols.TCP-based protocols.

And with additional And with additional downloaded software, downloaded software, elaborate Web sites that elaborate Web sites that include more than text include more than text and simple images can be and simple images can be accessed.accessed.


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HHyperyperTText ext TTransport ransport PProtocol rotocol

(HTTP)(HTTP)

<html><head><title>Welcome to IEEExpl</title></head> <body><table width="550" border="0" cellspacing="0" cellpadding="0" align="center"> <tr><td valign="top"> <img src="/images/subidinfmast_01.gif" width="550" height="39“ vspace="3" hspace="0" border="0" alt="IEEE xpl Subscription Access Information“ usemap="#Map"> <map name="Map"> <area shape="rect" coords="6,5,182,31" href="http://ieeexpl.ieee.org"> </map> <table width=510 border=1 cellspacing=0 cellpadding=5 bordercolor=#CCCCCC align=center><tr><td> Your institution subscribes to:</td></tr><tr><td bgcolor=#E8E8E8> Search Xplore Database</td></tr></table> <table width=510 border=1 cellspacing=0 cellpadding=5 bordercolor=#CCCCCC align=center><tr><td> Your institution subscribes to: </td> </tr> <tr> <td bgcolor=#E8E8E8> IEEE All Society Periodicals Package (ASPP) </td> </tr> <tr> <td bgcolor=#FFFFFF> <blockquote> <blockquote> Your online subscription includes access to the abstracts and full-text of IEEE journals, transactions, and magazines published since 1998: <a href=/xpl/ieeejrns.jsp?hr=1>IEEE journals, transactions, and magazines</a> </blockquote> </blockquote> </td> </tr> </table> <table width="500" border="0" cellspacing="0" cellpadding="0" align="center"><tr> <td> In addtion to the above, you may purchase individual IEEE journal/magazine articles and conference papers that are not included in your institution's online subscription. If you want a copy of an article or paper, first check with your librarian for a copy available locally. Any questions? <a href="/xpl/techform.jsp">Contact IEEE Customer Service</a>.</td></tr></table> <table width="500" border="0" cellspacing="0" cellpadding="0" align="center"> <tr> <td valign="top"> <div align="right"> <A href='javascript:window.close();'> <img src="/images/backbutton.gif" width="165" height="34" vspace="0" hspace="0" border="0" alt="Close this Window"></A> </div></td></tr></table></td></tr></table></body></html>

HTTP is the software defining the format of requests relayed from a HTTP is the software defining the format of requests relayed from a Web browser to a Web server, as well as the replies relayed from Web browser to a Web server, as well as the replies relayed from the server to the browser.the server to the browser.HTML (HyperText Markup Language) is the HTML (HyperText Markup Language) is the standard used to write Web pages; it doesn’t standard used to write Web pages; it doesn’t require specific formatting instructions, so two require specific formatting instructions, so two browsers may display a page differently.browsers may display a page differently.


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Extensible Markup Extensible Markup LanguageLanguage (XML)(XML)Unlike HTML, XML allows users to include content-Unlike HTML, XML allows users to include content-specific information in their files, facilitating its specific information in their files, facilitating its being formatted to suit various display devices.being formatted to suit various display devices.A job vacancy at the A job vacancy at the

department of Tourism is department of Tourism is added to the job database.added to the job database.

XML technology stores XML technology stores the data separately the data separately

from the presentation, from the presentation, allowing for a variety allowing for a variety

of platforms.of platforms.

The vacancy is The vacancy is displayed on the job displayed on the job

center kiosk...center kiosk...

...can be accessed ...can be accessed by mobile by mobile devices...devices...

...and is ...and is displayed on the displayed on the Department of Department of

Tourism Tourism website.website.


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Uniform Resource Locators Uniform Resource Locators (URLs)(URLs)A URL specifies three pieces of information:A URL specifies three pieces of information:

1. Type of file transfer 1. Type of file transfer 2. Name of computer 2. Name of computer 3. Name of file 3. Name of file

For example:For example:

http://www.cs.siue.edu/undergrad/BS/files/prerequisitehttp://www.cs.siue.edu/undergrad/BS/files/prerequisite

s.pdfs.pdf 1. http:// - type of file transfer 1. http:// - type of file transfer 2. cs.siue.edu - name of the computer 2. cs.siue.edu - name of the computer 3. /undergrad/BS/files/prerequisites.pdf - location of the file 3. /undergrad/BS/files/prerequisites.pdf - location of the file on the computeron the computer

Different types of file transfer:Different types of file transfer: http:// http:// - hypertext - hypertext

transfer protocol transfer protocol ftp:// ftp:// - file transfer protocol - file transfer protocol telnet:// telnet:// - opens a - opens a

telnet session telnet session gopher:// gopher:// - transfer file - transfer file

from a gopher server from a gopher server mailto:mailto: - open a mail - open a mail

sessionsession


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Network InterfaceNetwork Interface

HTTPHTTPClientClient

FTPFTPClientClient

BrowserBrowserControllerController

Client software runningClient software runningon the workstationon the workstation

JavaJavaInterpreterInterpreter

HTMLHTMLInterpreterInterpreter D

isp

lay D

river

Dis

pla

y D

river

Issuing Issuing requests for requests for external filesexternal files

Web BrowsingWeb Browsing

Input fromInput frommouse &mouse &keyboardkeyboard

CommunicationsCommunicationswith remotewith remoteWeb serverWeb server

Output toOutput touser’suser’sdisplaydisplay

InterpretingInterpretingdownloadeddownloadedWeb pagesWeb pagesand filesand files


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Internet Search EnginesInternet Search EnginesSearch engines use Search engines use “spider” programs to “spider” programs to “crawl” through the “crawl” through the Web, building a list of Web, building a list of words.words.

Some follow every link Some follow every link on every home page.on every home page.

Some ignore links that Some ignore links that lead to graphics, sound, lead to graphics, sound, or animation files, or to or animation files, or to newsgroups.newsgroups.

Some concentrate Some concentrate primarily on the most primarily on the most popular Web pages.popular Web pages.


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Comparing Search EnginesComparing Search Engines

Security IssuesSecurity IssuesRed = distribute adware, send Red = distribute adware, send

a high volume of spam, or a high volume of spam, or make unauthorized changes make unauthorized changes

to a user's computer to a user's computer Yellow = send a high volume Yellow = send a high volume

of "non-spammy" email, of "non-spammy" email, display many popup ads, or display many popup ads, or

prompt a user to change prompt a user to change browser settings browser settings

Share of SearchesShare of Searches

Chapter 16: The World Wide Web

Documents

world wide webpage

transfer file

world wide webchapter

type of file transfer

file transfer protocol

web browser

popular web pages

elaborate web sites