CE80N Introduction to Networks & The Internet Dr. Chane L. Fullmer UCSC Winter 2002

February 21, 2002CE80N -- Lecture #142 General Information TA Office… –Trailer #15 is no more –TA offices moved to the ISB Contact TA for current info…

February 21, 2002CE80N -- Lecture #143 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

February 21, 2002CE80N -- Lecture #144 Class Information Web page tutorial available on-line Web page submission: – to Subject: cmpe080n-assgn4 Final Exam –Last class session March 14, 2002

February 21, 2002CE80N -- Lecture #145 Personal Web Page of the Day No new pages received... So, here’s Venkatesh’s pageVenkatesh’s

February 21, 2002CE80N -- Lecture #147 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…

February 21, 2002CE80N -- Lecture #148 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.

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.

February 21, 2002CE80N -- Lecture #1410 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.

February 21, 2002CE80N -- Lecture #1411 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

February 21, 2002CE80N -- Lecture #1412 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

February 21, 2002CE80N -- Lecture #1413 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

February 21, 2002CE80N -- Lecture #1414 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

February 21, 2002CE80N -- Lecture #1415 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

February 21, 2002CE80N -- Lecture #1416 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

February 21, 2002CE80N -- Lecture #1417 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

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.

February 21, 2002CE80N -- Lecture #1419 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..

February 21, 2002CE80N -- Lecture #1420 “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.

February 21, 2002CE80N -- Lecture #1421 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

February 21, 2002CE80N -- Lecture #1422 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

February 21, 2002CE80N -- Lecture #1423 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

February 21, 2002CE80N -- Lecture #1424 Should You Accept Cookies? Cookies allow servers to tailor content to a particular user’s taste and needs. Rejecting cookies enforces anonymity.

February 21, 2002CE80N -- Lecture #1425 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

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.

February 21, 2002CE80N -- Lecture #1427 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

February 21, 2002CE80N -- Lecture #1428 Interesting Sites DataQuest USA Website Sun.com website

February 21, 2002CE80N -- Lecture #1429 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

February 21, 2002CE80N -- Lecture #1430 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

February 21, 2002CE80N -- Lecture #1431 Questions… Should you accept cookies? Why or why not? What is a plugin and how do you find the one you need?

February 21, 2002CE80N -- Lecture #1432 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.

February 21, 2002CE80N -- Lecture #1433 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

February 21, 2002CE80N -- Lecture #1435 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.

February 21, 2002CE80N -- Lecture #1436 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.

February 21, 2002CE80N -- Lecture #1437 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.

February 21, 2002CE80N -- Lecture #1438 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.

February 21, 2002CE80N -- Lecture #1439 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.