Today’s Lecture • Introduction to Computer networks and the WWW • Web search study Break • In-class activity – introduce your favorite/least favorite Web sites
A Review of Last Week’s Lecture • The Internet began as a military research project • It grew to its current role as a global communications network linking more than a billion persons, businesses, organizations, and governments. • The Internet has made information available on a scale never before imagined.
A Review of Last Week’s Lecture • The Internet is composed of interconnected client/server networks. • The Internet grew rapidly, especially after the Web became available as a new way of using the Internet. • There are several choices for bandwidth and pricing choices when connecting to the Internet.
Computer Networks • Network Interface Card (NIC):a card used to connect a computer to a network of other computers. • Server: computer that accepts requests and shares some or all of its resources with computers it is connected to. • NICs connect to cables which connect to servers.
The Internet • Computers connected to each other form a network. • LAN (localareanetwork): Networked computers physically near each other. • WAN (wideareanetwork): Networked computers not near each other.
A Client/Server LAN New Perspectives on The Internet, Sixth Edition—Comprehensive Appendix A 8
The Internet • internet: networks connected to each other • Internet: a specific internet that connects computers all over the world using a common set of interconnection standards (TCP/IP). • WorldWideWeb (WWW): a subset of the computers on the Internet that use software to make their contents easily accessible to each other.
The World Wide Web • Web servers: Computers connected to the Internet that contain files their owners have made available publicly through their Internet connections. • When you use your Internet connection to become part of the Web, your computer becomes a Webclient in a worldwide client/server network. • Web browser: software that you run on your computer to make it work as a Web client.
Client/Server Structure of the World Wide Web 11 New Perspectives on The Internet, Sixth Edition—Comprehensive Tutorial 1
Hypertext, Links, and Hypermedia • Hypertext Markup Language (HTML):standard language used on the Web to format documents. • HTML uses codes (tags) to tell the Web browser software how to display text. • <head> Heading new </head> • <body> This is the body text. </body> • HTML document: a text file that contains HTML tags. • When a Web browser displays an HTML document, it is referred to as a Webpage.
Hypertext, Links, and Hypermedia • HTML anchor tag: enables Web designers to link HTML documents to each other. (<A…> & </A>) • Hypertext links:can connect HTML documents together; can also connect one part of HTML document to another part. • Hypermedia links: hyperlinks that connect to computer files that contain pictures, graphics, and media objects such as sound and video clips.
Hypertext, Links, and Hypermedia New Perspectives on The Internet, Sixth Edition—Comprehensive Tutorial 1 14
Web Site Organization • Web site: a collection of linked Web pages with a common theme or focus. • Home page • the main page for a particular Web site. • the first page that opens when you start your Web browser; sometimes called start page. • the Web page that a Web browser loads the first time you use it; also sometimes called start page.
Addresses on the Web • Internet Protocol Address (IP): unique id number given to each computer on the Web. (i.e., 188.8.131.52) • Domain name: unique name associated with specific IP address by a program that runs on an Internet host computer. (www.cityu.edu.hk) • Domain Name Software (DNS): coordinates IP addresses and domain names for all computers attached to it. • Domain name server: the host computer that runs DNS software. • The last part of domain name is called its top-level domain (TLD).
Common Top Level Domains (TLDs) New Perspectives on The Internet, Sixth Edition—Comprehensive Tutorial 1 17
Uniform Resource Locators Four-part addressing scheme tells the Web browser: • Transfer protocol to use when transporting the file. • Domain name of computer on which file resides. • Pathname of folder or directory on computer on which file resides. • Name of the file.
Uniform Resource Locators Structure of a Uniform Resource Locator (URL)
Main Elements of Web Browsers • Title Bar • Scroll Bars • Status Bar • Menu Bar • Page Tab • Home Button
Finding Information on the Web Using Search Engines & Web Directories • Web Search Engines: Web pages that conduct searches of the Web to find words or expressions you enter. • Web Directory: a Web page that contains a list of Web page categories like education or recreation. Can narrow the results returned for a particular search. • Web directory editors categorize the Web pages.
Returning to Web PagesPreviously Visited • Using favorites and bookmarks • Internet Explorer - save the URL of a site you would like to revisit as a favorite in the Favorites folder. • Firefox - use a bookmark to save the URL of a specific page so you can return to it. • Using the History List • Back button • Forward button
Returning to Web PagesPreviously Visited • Cookie • A small file that a Web server writes to the disk of the client computer. • Can contain information about the user such as login names and passwords. • Assists in performing functions such as automatic login. • User is often unaware that the files are being written to the computer’s disk drive.
Reloading a Web Page and Stopping a Web Page Transfer • The browser stores a copy of every Web page it displays on your computer’s hard drive in a cache folder. • Use the Refresh button in IE or the Reload button in Firefox to load the same Web page that appears in the browser window again. • Use the Stopbutton to halt the Web page transfer from the server.
Printing and Saving Web Pages • You can use a Web browser to print a Web page. • You can save copies of most Web pages as files that you can store on your computer’s hard disk, floppy disk, etc. • Some Web pages are written to make copying and saving difficult or impossible.
Examining Additional Web Browser Choices • Other Internet browsers began to make a dent in Microsoft’s dominant position in 2004. • Security flaws in Internet Explorer were increasingly exploited by virus and worm writers. • Organizations and individuals began to doubt reliability of a single browser. • http://en.wikipedia.org/wiki/Comparison_of_web_browsers
Mozilla Project • Mosaic • One of the first Web browsers • Developed in 1990s • NetscapeNavigator • First commercially successful Web browser • Created by Mosaic developers • Originally called “Mozilla,” short for “Mosaic killer”
Mozilla Project • Mozilla project • Started in 1999 after Netscape Navigator was turned over to a non-profit organization • They rebuilt the browser rendering engine (the internal workings of the browser) • Gecko engine: browser rendering engine used in Netscape Navigator, the Mozilla browser and Mozilla Firefox.
Mozilla Suite • A combination of software applications developed by the Mozilla open source project. • Web browser • E-mail client and newsreader – Mozilla Messenger • HTML editor – Mozilla Composer • Instant messaging chat client – ChatZilla • Time Warner’s AOL division distributes most of the Mozilla Suite as Netscape Navigator.
Browsers for Hire:Opera and iRider • Internet Explorer, Navigator, Mozilla, and Firefox are all available at no cost. • Some browsers, such as Opera and iRider, charge a license fee
Opera • Started out as research project at Telenor, Norway’s state telecommunication company. • Program code written independently and is not affected by security flaws exploited by those attacking Gecko-based browsers or IE. • Free version available supported by advertising.
Opera for Mobile • Gives mobile device users a fully functional Web browser. • Users can view any Web site (not just those designed to display on mobile devices) using a mobile phone, PDA, or similar device.
Opera Web Browser Main Screen New Perspectives on The Internet, Sixth Edition—Comprehensive Tutorial 1 33
iRider • Designed for power users. • Can view thumbnail images of multiple open Web pages displayed in a hierarchical map called a Page List. • Keeps all open Web pages in memory until the user deletes them. • User can run several searches simultaneously and compare the results. • Users can select multiple links on a page and iRider downloads the pages simultaneously.
Multiple Searches in the iRider Web Browser Hierarchy of thumbnail images (one for each Web page visited). New Perspectives on The Internet, Sixth Edition—Comprehensive Tutorial 1 35
Reproducing Web Pages and Copyright Law • Copyright: Legal right of the author or other owner of an original work to control reproduction, distribution and sale of that work. • Laws govern the use of photocopies, audio or video recordings, and other reproductions of authors’ original work. • Comes into existence as soon as the work is placed into tangible form. • Exists even if the work does not contain a copyright notice.
Reproducing Web Pages and Copyright Law • Fair use is a provision that allows students to use limited amounts of copyrighted information in term papers and other reports in an academic setting. • Source must always be cited. • Commercial use of copyright more restricted. • Obtain permission from copyright holder before using anything you copy from a Web page.
Checking Web Page Security (IE) • A closed padlock symbol (security indicator button) appears in the status bar when Internet Explorer loads an encrypted Web page. • Encryption is a way of scrambling and encoding data transmissions that reduces the risk that a person who intercepts the Web page as it travels across the Internet will be able to decode and read the page’s contents. • To check some of the security elements of a Web page, • double-click the security indicator button • click File, Properties, and then click the Certificates button
Using Internet Explorer toSave a Web Page • You can save entire Web pages, selected portions of Web page text, or particular graphics from a Web page to a disk. • You can save portions of Web page text so you can use it in other programs. • You can save a graphic from a Web page by right-clicking on the picture and clicking Save Picture As.
Checking Web Page Security (Firefox) • A closed padlock symbol (the security indicator button) appears in the status bar when Firefox loads an encrypted Web page. • Encryption is a way of scrambling and encoding data transmissions that reduces the risk that a person who intercepts the Web page as it travels across the Internet will be able to decode and read the page’s contents. • To check some of the security elements of a Web page, • double-click the security indicator button • click Tools, Page Info, and then click the Security tab
Managing Cookies (Firefox) • Firefox stores all cookies in one file and gives users a tool to manage that file. • Click Tools on the menu bar, click Options, click the plus sign next to Cookies. • Click the View Cookies button to view individual cookies. • Select a cookie, and then click the Remove Cookie button to delete it. • To delete all cookies that have been stored on your computer, click the RemoveAllCookies button.
Using Firefox to Save a Web Page • You can store entire Web pages, selected portions of Web page text, or particular graphics from a Web page to a disk. • You can save portions of Web page text so you can use it in other programs. • You can save a graphic from a Web page by right-clicking on the picture and clicking Save Image As.
Summary • Web pages and Web sites make up the World Wide Web. • The Web uses a client/server structure in which Web server computers make Web page files available to Web client computers that are running Web browser software. • Each server computer on the Internet has an IP address that is mapped to a domain name. • The domain name plus the Web page filename make up the Uniform Resource Locator (URL).
Summary • All Web browsers have the same basic elements and can be used to explore the Web in similar ways. • Web browsers display Web pages and maintain a history list that can be used to find pages previously visited. • Web browsers allow users to print and save Web pages and elements of Web pages. • Web browsers are currently available at no or low cost.
Summary • The two most widely used Web browsers are • Internet Explorer • Firefox
How to access newmedia server • http://newmedia.cityu.edu.hk/en3515/
Exercise 1: my favorite Web sites My favorite sites http://www.wikipedia.org http://www.google.com www.nytimes.com www.flickr.com hk.yahoo.com
Exercise 2: Use WWW to research following technologies What should you do? • Form a group • Pick a topic from the list to the left • Using WWW to conduct a research on this topic and answer the following questions: • What is it? • How does it work? • What are some of the advantages of using it? • What are some of the disadvantages of using it? • Are there any social controversy associated with it? • What do you think about it? Note: keep detailed notes. Be prepared to give a presentation on the topic next week. • Wikis • Server side technologies • Dynamic Web sites • Widgets • Phishing • Podcasts • facebook.com • Ubiquitous computing • Search engine Bots/Spiders • PGP (Pretty Good Privacy) • W3C