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1. Unit-V
World Wide Web

2.  World Wide Web IS an architectural framework for accessing linked documents
called web pages that are spread over thousand of computers all over the world.
 WWW is a set of programs, standards and protocols that allow the text, images,
animations, sounds and videos to be stored, accessed and linked together in form of
web sites.
 The WWW project was developed at CERN, the European Center for Nuclear
Research in 1989.
 It has a unique combination of flexibility, portability, and user-friendly features that
distinguishes it from the other services provided by the Internet.
World Wide Web

3.  WWW is basically a distributed client-server service. It this, a client can access the services from a server using a browser.
 These services are usually distributed over many locations called sites or websites.
 From the user's point of view web consists of a vast worldwide collection of documents called web pages. These web pages
reside on different sites or machines all over the world.
 Each web page can contain link to other pages any where in the world. By clicking on such link user can access another web
page.
 This kind of link can be in form of string of text or picture, sound, movie clip etc.
 Such a text or image that enables the user to link to another web page is called hyperlink.
WWW Architecture

5.  The string of text that points to another web page is called hypertext. The difference between the
normal text and hypertext is that, when you take the mouse pointer over it, it changes into a hand
shaped cursor. Such a text is sometime, underlined and blue is colour.
 Hypermedia is enhanced form of a hyperlink which not only links to the other pages or other sections
within the same page but can also link with various medium like sound, animation, movie clip etc,
Hypermedia is grouping of different media like sound, graphics, animations and text in a single file.
 These hyperlinks are created with the help of specialized language called Hypertext Mark up Language
(HTML).
 In order to access these web pages on different sites, each of these pages has a specific address called
Uniform Resource Locator (URL).
 Web pages are viewed with a program called a browser.
WWW Architecture

6.  web page is a document available on world wide web. Web Pages
are stored on web server and can be viewed using a web browser.
 A web page can contain huge information including text, graphics,
audio, video and hyper links. These hyper links are the link to
other web pages.
Web Page

7.  Static web pages are also known as flat or stationary web page.
They are loaded on the client’s browser as exactly they are stored
on the web server. Such web pages contain only static
information. User can only read the information but can’t do any
modification or interact with the information.
 Static web pages are created using only HTML. Static web pages
are only used when the information is no more required to be
modified.
Static Web page

8.  SERVER-SIDE DYNAMIC WEB PAGE
 It is created by using server-side scripting. There are server-side
scripting parameters that determine how to assemble a new web
page which also include setting up of more client-side processing.
 CLIENT-SIDE DYNAMIC WEB PAGE
 It is processed using client side scripting such as JavaScript. And then
passed in to Document Object Model (DOM).
Dynamic Web page

9.  web Browser is an application software that allows us to view and
explore information on the web. User can request for any web
page by just entering a URL into address bar.
 Web browser can show text, audio, video, animation and more. It
is the responsibility of a web browser to interpret text and
commands contained in the web page.
Web Browser

10. Browser Vendor
Internet Explorer Microsoft
Google Chrome Google
Mozilla Firefox Mozilla
Netscape Navigator Netscape Communications Corp.
Opera Opera Software
Safari Apple
Sea Monkey Mozilla Foundation
K-meleon K-meleon
Web Browser

11. Web Browser Architecture

12.  The user interface: this includes the address bar, back/forward button, bookmarking menu, etc. Every part of the browser
display except the window where you see the requested page.
 The browser engine: marshals actions between the UI and the rendering engine.
 The rendering engine : responsible for displaying requested content. For example if the requested content is HTML, the
rendering engine parses HTML and CSS, and displays the parsed content on the screen.
 Networking: for network calls such as HTTP requests, using different implementations for different platform behind a
platform-independent interface.
 UI backend: used for drawing basic widgets like combo boxes and windows. This backend exposes a generic interface that is
not platform specific. Underneath it uses operating system user interface methods.
 JavaScript interpreter. Used to parse and execute JavaScript code.
 Data storage. This is a persistence layer. The browser may need to save all sorts of data locally, such as cookies. Browsers
also support storage mechanisms such as localStorage, IndexedDB, WebSQL and FileSystem.
The browser's high level structure

13.  “bridge” between user interface (UI) and rendering engine
 plug-ins
 extensions
 add-ons
Browser Engine

14.  Able to render the content available of the Web – representations
of resources (e.g., HTML documents)
 Processing the DOM tree corresponding to a Web page
 By applying the CSS style properties in order to render
information within a display area – viewport sources (e.g., HTML
documents)
Rendering Engine

15.  Gecko (Firefox)
 Presto (Opera)
 Trident (MSIE)
 WebKit (Chrome, Safari, iOS)
Rendering Engine Examples

16.  Because – usually – CSS styles do not modify the DOM tree, the
rendering process is not dependent by the loading of CSS files.
 The processing is made in a synchronous manner .
 JavaScript programs must be executed immediately when the engine
spots the JS source-code (eventually, loaded from an external URL) .
 implicitly, the rendering process is stopped until the JavaScript code is
entirely executed
Rendering Engine

17.  Web server is a computer where the web content is stored.
Basically web server is used to host the web sites but there exists
other web servers also such as gaming, storage, FTP, email etc.
 Web site is collection of web pages while web server is a software that
respond to the request for web resources.
Web Server

18. S.N. Web Server Descriptino
1 Apache HTTP Server
This is the most popular web server in the world developed by the Apache Software Foundation.
Apache web server is an open source software and can be installed on almost all operating systems
including Linux, UNIX, Windows, FreeBSD, Mac OS X and more. About 60% of the web server
machines run the Apache Web Server.
2. Internet Information Services (IIS)
The Internet Information Server (IIS) is a high performance Web Server from Microsoft. This web
server runs on Windows NT/2010 and 2012 platforms (and may be on upcoming new Windows
version also). IIS comes bundled with Windows; Because IIS is tightly integrated with the operating
system so it is relatively easy to administer it.
Example

19.  When client sends request for a web page, the web server search
for the requested page if requested page is found then it will send
it to client with an HTTP response.
 If the requested web page is not found, web server will the send
an HTTP response:Error 404 Not found.
 If client has requested for some other resources then the web
server will contact to the application server and data store to
construct the HTTP response.
Web Server Working

20.  Search Engine refers to a huge database of internet resources such
as web pages, newsgroups, programs, images etc. It helps to
locate information on World Wide Web.
 User can search for any information by passing query in form of
keywords or phrase. It then searches for relevant information in its
database and return to the user.
Search Engine

21.  Generally there are three basic components of a search engine as
listed below:
 Web Crawler
 Database
 Search Interfaces
Search Engine Components

22.  Web crawler
 It is also known as spider or bots. It is a software component that traverses the web to
gather information.
 Database
 All the information on the web is stored in database. It consists of huge web resources.
 Search Interfaces
 This component is an interface between user and the database. It helps the user to
search through the database.
Search Engine Components

23.  Web crawler, database and the search interface are the major
component of a search engine that actually makes search engine
to work. Search engines make use of Boolean expression AND, OR,
NOT to restrict and widen the results of a search. Following are
the steps that are performed by the search engine:
Search Engine Working

24.  The search engine looks for the keyword in the index for predefined
database instead of going directly to the web to search for the
keyword.
 It then uses software to search for the information in the database. This
software component is known as web crawler.
 Once web crawler finds the pages, the search engine then shows the
relevant web pages as a result. These retrieved web pages generally
include title of page, size of text portion, first several sentences etc.
Search Engine Working