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CE80N Introduction to Networks & The Internet

CE80N Introduction to Networks & The Internet. Dr. Chane L. Fullmer UCSC Winter 2002. General Information. TA Office… Trailer #15 is no more TA offices moved to the ISB Contact TA for current info…. Web Search based Essay. Essay based on Web search results

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CE80N Introduction to Networks & The Internet

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  1. CE80NIntroduction to Networks&The Internet Dr. Chane L. Fullmer UCSC Winter 2002

  2. General Information • TA Office… • Trailer #15 is no more • TA offices moved to the ISB • Contact TA for current info… CE80N -- Lecture #14

  3. Web Search based Essay • Essay based on Web search results • 1-2 pages on any topic of interest • Must include results from at least four Web page references • References must be listed in a bibliography • Due Tuesday, February 26, 2002 CE80N -- Lecture #14

  4. Class Information • Web page tutorial available on-line • Web page submission: • Email to venkat@cse.ucsc.edu • Subject: cmpe080n-assgn4 • Final Exam • Last class session • March 14, 2002 CE80N -- Lecture #14

  5. Personal Web Page of the Day • No new pages received... • So, here’s Venkatesh’s page CE80N -- Lecture #14

  6. Conventional Web Pages Are Static • Web pages that do not change are called static or passive. • Fixed by author • Remains unchanged until author changes it • Most web pages are static… CE80N -- Lecture #14

  7. How A Server Stores Static Web Pages • Making information available on the WWW: • Requires a computer with a disk • Requires a permanent connection to the Internet • Someone, somewhere is on-line on the Internet, 24/7 • Requires web server software • Servers are passive. Waiting for browsers to contact it. CE80N -- Lecture #14

  8. Figure 24.1 Figure 24.1 (a) A user enters a URL, causing a browser to contact a Web server and request the item, and (b) the server extracts the specified item from its local disk and sends a copy to the browser.

  9. Fetching Items One At A Time • Pages and images are stored separately. • Allows user to have more control • Can display the page without images • Important for dial-up modems • Gives user time to read the text before loading the images • Useful for visually impaired, text can be converted to speech by software. CE80N -- Lecture #14

  10. Conventional Web Pages Use The Entire Screen • Each new page completely replaces the previous page. • Can be inconvenient • Must return to original page to see additional links CE80N -- Lecture #14

  11. A Web Page Can Change Part Of The Screen • Frame Technology • Partitions page into independent regions. • Frames allow users to change the display in one region without affecting another. • Example Page with Frames CE80N -- Lecture #14

  12. Static Documents Have Disadvantages • Static web pages remain popular because they: • Are easy to create • Are inexpensive to maintain • Can be retrieved quickly • A major disadvantage is that the user cannot interact with the page. • Commercial web sites tend to use frames CE80N -- Lecture #14

  13. Controlling How A Browser Processes Data • Images and sounds must be treated differently. • Multiple images can be displayed to the screen simultaneously • Audio is played one clip at a time through the system speakers • No single standard exists for storing digitized audio clips. • No standardized audio/video hardware available – still changing and evolving CE80N -- Lecture #14

  14. Plugins Allow Variety • A plugin is a small program that knows how to interpret one specific data format. • Must know how to use audio/video hardware to convert the digitized information • Must be downloaded to extend the browser • Example PlugIn -- Real Audio CE80N -- Lecture #14

  15. A Server Can Compute A Web Page On Demand • Common Gateway Interface (CGI) makes it possible for Web pages to have dynamic content. • Allows the Web server to associate a URL with a program instead of a Web page • Allows dynamic information to be displayed, based on current information • Current Temperature, current inventory • Counters – ie, page access CE80N -- Lecture #14

  16. How CGI Works • Requests for static documents and CGI output have the same syntactic form. • The browser isn’t told if it is: • Returning a copy of a static document or • Returning the output from a CGI program CE80N -- Lecture #14

  17. Figure 24.3 Figure 24.3 (a) A browser requests a URL that corresponds to a CGI program, causing the server to start the program, and (b) the CGI program computes a response, which the server returns to the browser.

  18. Professional Programmers Build CGI Programs • CGI programs must be: • Written by programmers • Written for specific servers • Apache, Netscape, M$ IE • Written with the operating system in mind • Unix, Macintosh, M$ Windows. Etc.. CE80N -- Lecture #14

  19. “Personalizing” Web Content • If the server has personal information about the user, CGI can be used to “personalize” the page content. • Based on a current set of preferences • Stock quotes • Advertising based on customer personal info, or past preferences. CE80N -- Lecture #14

  20. Web Pages Can Interact • FORMS Technology • Forms permit a web page to have blank areas in which the user must enter information. • Makes it possible to enter data directly • Name, address, credit card info… • Allows information to be sent to the server directly CE80N -- Lecture #14

  21. Shopping Carts • Shopping carts are used by commercial Web sites that sell products. • Can add items to the shopping cart • Keeps a list of all items the user adds to the the cart • Can maintain the list for a specified number of days CE80N -- Lecture #14

  22. Cookies • Identification numbers that a browser and server exchange are called cookies. • Assigned a value by the server and stored on user’s computer • Stores additional information on the server • Just a little bit about you for our files…  • Uses the cookie to retrieve the information from its database CE80N -- Lecture #14

  23. Should You Accept Cookies? • Cookies allow servers to tailor content to a particular user’s taste and needs. • Rejecting cookies enforces anonymity. CE80N -- Lecture #14

  24. Active Documents Are More Powerful • A browser receives a copy of an active document from the server but runs it on the local computer. • Performs computation on the user’s computer • Does not depend on the Web server for computational needs CE80N -- Lecture #14

  25. Figure 24.4 (a) A browser requests a URL that corresponds to an active document, and (b) the browser runs a copy of the active document, which then controls the screen.

  26. Java Is An Active Document Technology • Java calls an active document an applet. • Created to make the Java language similar to a widely-used programming language (C++) • Java was the first active document technology • The Java system includes common task software, making applet creation quick. • Provides more functionality than most other technologies • Java provides for high quality animations CE80N -- Lecture #14

  27. Interesting Sites • DataQuest USA Website • Sun.com website CE80N -- Lecture #14

  28. JavaScript Is An Active Document Technology • JavaScript can be embedded in a standard HTML file. • Simpler to use than Java • A browser: • Performs the specified computation • Displays the results • Offers similar functionality as Java CE80N -- Lecture #14

  29. The Importance of Advanced Web Technologies • Active document technologies like Java and JavaScript are gaining in popularity. • Does not require faster servers • Appears to make objects move smoothly CE80N -- Lecture #14

  30. Questions… • Should you accept cookies? Why or why not? • What is a plugin and how do you find the one you need? CE80N -- Lecture #14

  31. Summary • Web pages can be static or dynamic • Frame technology allows for regions on a page to display independently • Common Gateway Interface (CGI) allows for dynamic pages • FORMS technology allows for interaction with web pages. CE80N -- Lecture #14

  32. Summary… • Shopping carts allow for intermittent shopping on-line.. • Cookies.. Information exchanged between your system and theirs… • Should you always allow cookies ? • Active documents – a program to run locally from your browser.. • Java programming language • JavaScript CE80N -- Lecture #14

  33. Glossary • Archie • An early automated internet search service that could find all files with a given name. • Automated Search • Any service that locates information without requiring the user to make decisions or select from menus. CE80N -- Lecture #14

  34. Glossary • CGI • (Common Gateway Interface) A technology that uses a computer program to assemble a Web page whenever a user request the page. • Cookie • A small amount of data (usually a string of less than 50 characters) used to identify a World Wide Web user. CE80N -- Lecture #14

  35. Glossary • JAVA • A programming language developed by Sun Microsystems used to create active Web pages • JavaScript • A programming language used to create active Web pages that is simpler (and less powerful) than Java. CE80N -- Lecture #14

  36. Glossary • Navigating (the Internet) • A phrase used by the popular press that means, “using Internet services to browse information.” • Search Key • A string of characters that a user provides to a search service. CE80N -- Lecture #14

  37. Glossary • Search Tool • Any program that permits a user to find the location of information. • Shopping Cart • A mechanism used on the World Wide Web to allow someone to select multiple items from an online catalog before they make a purchase. CE80N -- Lecture #14

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