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– http is the protocol– www.microsoft.com is the server name– /office is the file on that server

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

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)

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”

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

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

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.

Plug-ins and Helper Applications View plug-ins:

Tools->Internet Options->

_General->Settings->View objects_

Programs tab File extension mechanism

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

VRML

3D environments Usually done as a plugin .wrl extension

Browser Features Top tool bar

– Back , forward– Refresh , update local copies– Home ; set home page Tools->Internet Options

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

Cache and Refresh Browsers copy html files to

local disk and retrieve from the stored copy

Change Cache settingsTools->Internet Options-> temporary

internet files-> settings

Location example:C:\Documents and Settings\userID\Local

Settings\Temporary Internet Files

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

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

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

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”

Saving and Viewing Information

View->refresh File ->Print File->save As Save Image

– Right click on image, save as

View->source

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

Example: Amazon.com

Https:// and lock icon when using secure server, http:// and no lock icon or unlocked lock icon for unsecure server

Warning

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

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

Browser

(netscape)

WWW Server

(apache)

httprequest

response

HTTP(cont)

Request

Method URL HTTP Version

Response Mime like Status codesExample: 302-moved

Main Methods: GET, HEAD, POST

Others; Put, Patch, copy, move, delete, link, unlink, option

Status line

Headers

A blank line

Body if required

HTTP example

client

server

GET /usr/bin/image1 HTTP1.1Accept: image/gif

HTTP/1.1 200 OKDate: mon, 07-jan-02 13:15:14: GMTServer: ChallangerMIME-Version: 1.0Content-Length:2048( body of document)