ce80n introduction to networks & the internet

CE80NCE80NIntroduction to NetworksIntroduction to Networks

&&The InternetThe Internet

Dr. Chane L. Fullmer

UCSC

Winter 2002

February 21, 2002 CE80N -- Lecture #14 2

General InformationGeneral Information

TA Office…– Trailer #15 is no more– TA offices moved to the ISB

• Contact TA for current info…


Web Search based EssayWeb 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


Class InformationClass InformationWeb page tutorial available on-lineWeb page submission:

– Email to [email protected]• Subject: cmpe080n-assgn4

Final Exam – Last class session

• March 14, 2002

mailto:[email protected]


Personal Web Page of the DayPersonal Web Page of the Day

No new pages received...So, here’s Venkatesh’s page

http://www.cse.ucsc.edu/~venkat


Conventional Web Pages Are Conventional Web Pages Are StaticStatic

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…


How A Server Stores Static Web How A Server Stores Static Web PagesPages

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 24.1Figure 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.


Fetching Items One At A TimeFetching 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.


Conventional Web Pages Use Conventional Web Pages Use The Entire ScreenThe Entire Screen

Each new page completely replaces the previous page.– Can be inconvenient– Must return to original page to see

additional links


A Web Page Can Change Part Of A Web Page Can Change Part Of The ScreenThe 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

http://www.cse.ucsc.edu/research/ccrg/cpt2.7classes/cruznFrames.html


Static Documents Have Static Documents Have DisadvantagesDisadvantages

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


Controlling How A Browser Controlling How A Browser Processes DataProcesses 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


Plugins Allow VarietyPlugins 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

http://www.kpig.com/




A Server Can Compute A Web A Server Can Compute A Web Page On DemandPage 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


How CGI WorksHow 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 24.3Figure 24.3Figure 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.


Professional Programmers Build Professional Programmers Build CGI ProgramsCGI 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..


““Personalizing” Web ContentPersonalizing” 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.


Web Pages Can InteractWeb 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


Shopping CartsShopping 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


CookiesCookies

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


Should You Accept Cookies?Should You Accept Cookies?

Cookies allow servers to tailor content to a particular user’s taste and needs.

Rejecting cookies enforces anonymity.


Active Documents Are More Active Documents Are More PowerfulPowerful

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.


Java Is An Active Java Is An Active Document TechnologyDocument 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


Interesting SitesInteresting Sites

DataQuest USA WebsiteSun.com website

http://www.dqusa.com/

http://www.dqusa.com/

http://www.sun.com/


JavaScript Is An Active JavaScript Is An Active Document TechnologyDocument 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


The Importance of Advanced The Importance of Advanced Web TechnologiesWeb Technologies

Active document technologies like Java and JavaScript are gaining in popularity.– Does not require faster servers– Appears to make objects move

smoothly


Questions…Questions…

Should you accept cookies? Why or why not?

What is a plugin and how do you find the one you need?


SummarySummary

Web pages can be static or dynamicFrame technology allows for regions

on a page to display independentlyCommon Gateway Interface (CGI)

allows for dynamic pagesFORMS technology allows for

interaction with web pages.


Summary…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


GlossaryGlossary

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.


GlossaryGlossary

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.


GlossaryGlossary

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.


GlossaryGlossary

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.


GlossaryGlossary

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.