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Web Browsers

Web Browsers. CS 3505. Wb_webBrowsers-I.ppt. Vendors. Major web browsers: Netscape and Microsoft IE, Firefox , Opera 8 AOL uses a browser that’s re-branded IE (I think). They’re free A few others out there: lynx (text-based), etc. URLs. The URL: http://www.microsoft.com/office

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Web Browsers

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  1. Web Browsers CS 3505 Wb_webBrowsers-I.ppt

  2. Vendors • Major web browsers: Netscape and Microsoft IE, Firefox , Opera 8 • AOL uses a browser that’s re-branded IE (I think). • They’re free • A few others out there: lynx (text-based), etc

  3. URLs • The URL: http://www.microsoft.com/office • http is the protocol • www.microsoft.com is the server name • /office is the file on that server

  4. URLs • ftp://ftp. nps.navy.mil/ • ftp is the protocol • ftp.nps.navy.mil is the server • Logs you onto the ftp server as user “anonymous” with ?? As password. NPS FTP does not work well try ftp://ftp.microsoft.com

  5. URLs • news://news.mbay.net • news/nntp is the protocol • news.mbay.net is the news server • Launches news reader • gopher:// hardly ever used these days • https:// is secure http (more later)

  6. What the URL means • Http: “Using the http protocol” • machine name: “Connect to this machine” • file name: “starting from the default point for documents on this web server, retrieve this document”

  7. URL Example • Example: http://www.nps.navy.mil/cs/Faculty.asp • On the site www.nps.navy.mil, the Web server will look for the file • CS/Faculty.asp

  8. Default index file • Usually you can just specify the directory you want to look in. By default the server will look for a file usually called “index.html” within that directory. • Index.html or default html is usually the top file of a web site • Also htm and html are alternative dialects

  9. Other types of files • You can configure your web browser to cooperate with types of files other than html • You can configure it to launch a “helper application” or “plugin” when it encounters a file. A plugin is a program that runs inside of your browser. A helper application launches external to the web browser.

  10. Plug-ins and Helper Applications • View plug-ins: Tools->Internet Options-> _General->Settings->View objects_ • Programs tab • File extension mechanism

  11. PDF • Adobe Portable Document Format • Postscript-like control of graphics in the document • Free viewer from adobe • Can either be viewed as a plugin or an external viewer

  12. VRML • 3D environments • Usually done as a plugin • .wrl extension

  13. Browser Features • Top tool bar • Back , forward • Refresh , update local copies • Home ; set home page Tools->Internet Options

  14. Bookmarks • An easy way to save a place on the web • Called “Favorites” in Internet Explorer • “History” provides a list of sites visited • Today,Last week, 2 weeks,3weeks

  15. Cache and Refresh • Browsers copy html files to local disk and retrieve from the stored copy • Change Cache settings Tools->Internet Options-> temporary internet files-> settings • Location example: C:\Documents and Settings\userID\Local Settings\Temporary Internet Files

  16. Searching the web • Click “Search” on IE • Enter key words on pop up • Uses MS Search engine • Go to A search engine • Yahoo.com, AltaVista.com, Google.com • Enter key words

  17. Key word searches • Return all key words • Example:Terrain Images • Will return references to all indexed pages which contain the word • Terrain • Images • Lots of “hits” • Presented in an order as determined by the search engines “evaluator rules” • Often paid advertisements are the primary order • Yahoo was “pure” until recently

  18. Advanced Boolean searches • Most search engines have Boolean rules usually available through a help or advanced search button • Typical Advances search options • Match all words(AND) • Match any words(OR) • Group whole phrase(“ “) • Do not include (NOT) • Example Yahoo the OR is implicitly coded as a blank • Natural gas prices in Washington State • Will get hits on all words except articles(in, a, of..) • Reduce the search by applying rules • “Natural gas prices” “Natural gas cost” Washington NOT DC

  19. Search Trick * Often the whole or part of a web page has been indexed thus one is searching for a phrase in a page. * Think how the question would be answered not how it would be asked * NOT “What is the capital of Ohio” *Instead “The capital of Ohio is”

  20. Saving and Viewing Information • View->refresh • File ->Print • File->save As • Save Image • Right click on image, save as • View->source

  21. Secure Transmission • Recall that messages and files sent across the internet are plain text and can be intercepted • SSL uses encryption to send files and messages across the net. This is done with secure http, https. • A bit slower than http, but fast enough • https and a little icon of a lock show you’re secure

  22. Example: Amazon.com • Https:// and lock icon when using secure server, http:// and no lock icon or unlocked lock icon for unsecure server • Warning

  23. Cookies • Cookies are used to implement things like shopping carts • Web servers can’t remember information from one transaction to the next easily. • Cookies are just a place for a web server to store data • Location example: C:\Documents and Settings\userID\cookies • Control Coockies: tools->internet options-> Security-> custom level

  24. HTTP • Http is the protocol used by browsers and servers on the web • Very simple request response sequence • RFC 2616: Hypertext Transfer Protocol -- HTTP/1.1 http WWW Server (apache) Browser (netscape) request response

  25. Status line Headers A blank line Body if required HTTP(cont) • Request Method URL HTTP Version Main Methods: GET, HEAD, POST Others; Put, Patch, copy, move, delete, link, unlink, option • Response • Mime like • Status codes Example: 302-moved

  26. HTTP example client server GET /usr/bin/image1 HTTP1.1 Accept: image/gif HTTP/1.1 200 OK Date: mon, 07-jan-02 13:15:14: GMT Server: Challanger MIME-Version: 1.0 Content-Length:2048 ( body of document)

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