Chapter 16: The World Wide Web

Chapter 16: The World Wide Web The World Wide Web applies point-and-click hypermedia application software to facilitate accessing documents on the Internet via TCP-based protocols. Click on this piece of hypertext, and you’re taken to... Type in a keyword and click the “Go!” pushbutton, and you’re taken to... And with additional downloaded software, elaborate Web sites that include more than text and simple images can be accessed. Click on this pushbutton, and you’re taken to... Chapter 16 The World Wide Web Page 189

HyperTextTransport Protocol (HTTP) 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 the server to the browser. HTML (HyperText Markup Language) is the standard used to write Web pages; it doesn’t require specific formatting instructions, so two browsers may display a page differently. <html><head><title>Welcome to IEEExpl</title></head> <body> <table width="550" border="0" cellspacing="0" cellpadding="0" align="center"> <tr><td valign="top"> <imgsrc="/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();'> <imgsrc="/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> Chapter 16 The World Wide Web Page 190

Extensible Markup Language(XML) Unlike HTML, XML allows users to include content-specific information in their files, facilitating its being formatted to suit various display devices. A job vacancy at the department of Tourism is added to the job database. XML technology stores the data separately from the presentation, allowing for a variety of platforms. Chapter 16 The World Wide Web Page 191 The vacancy is displayed on the job center kiosk... ...can be accessed by mobile devices... ...and is displayed on the Department of Tourism website.

Uniform Resource Locators (URLs) A URL specifies three pieces of information: 1. Type of file transfer 2. Name of computer 3. Name of file Different types of file transfer: http:// - hypertext transfer protocol ftp:// - file transfer protocol telnet:// - opens a telnet session gopher:// - transfer file from a gopher server mailto: - open a mail session For example: http://www.cs.siue.edu/undergrad/BS/files/prerequisites.pdf 1. http:// - type of file transfer 2. cs.siue.edu - name of the computer 3. /undergrad/BS/files/prerequisites.pdf - location of the file on the computer Chapter 16 The World Wide Web Page 192

Web Browsing Browser Controller Client software running on the workstation HTML Interpreter Display Driver Java Interpreter HTTP Client FTP Client Network Interface Interpreting downloaded Web pages and files Input from mouse & keyboard Output to user’s display Issuing requests for external files Communications with remote Web server Chapter 16 The World Wide Web Page 193

Internet Search Engines Search engines use “spider” programs to “crawl” through the Web, building a list of words. Some follow every link on every home page. Some ignore links that lead to graphics, sound, or animation files, or to newsgroups. Some concentrate primarily on the most popular Web pages. Chapter 16 The World Wide Web Page 194

Comparing Search Engines Share of Searches Security Issues Red = distribute adware, send a high volume of spam, or make unauthorized changes to a user's computer Yellow = send a high volume of "non-spammy" email, display many popup ads, or prompt a user to change browser settings Chapter 16 The World Wide Web Page 195

Chapter 16: The World Wide Web